bug: implement comment edition

- add a new operation
- add a new "timeline" in the snapshot that hold a processed version of the operations

23 files changed, 4196 insertions, 0 deletions

diff --git a/vendor/github.com/google/go-cmp/LICENSE b/vendor/github.com/google/go-cmp/LICENSE
new file mode 100644
index 00000000..32017f8f
--- /dev/null
+++ b/vendor/github.com/google/go-cmp/LICENSE
@@ -0,0 +1,27 @@
+Copyright (c) 2017 The Go Authors. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+   * Redistributions of source code must retain the above copyright
+notice, this list of conditions and the following disclaimer.
+   * Redistributions in binary form must reproduce the above
+copyright notice, this list of conditions and the following disclaimer
+in the documentation and/or other materials provided with the
+distribution.
+   * Neither the name of Google Inc. nor the names of its
+contributors may be used to endorse or promote products derived from
+this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/vendor/github.com/google/go-cmp/cmp/compare.go b/vendor/github.com/google/go-cmp/cmp/compare.go
new file mode 100644
index 00000000..7e215f22
--- /dev/null
+++ b/vendor/github.com/google/go-cmp/cmp/compare.go
@@ -0,0 +1,553 @@
+// Copyright 2017, The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE.md file.
+
+// Package cmp determines equality of values.
+//
+// This package is intended to be a more powerful and safer alternative to
+// reflect.DeepEqual for comparing whether two values are semantically equal.
+//
+// The primary features of cmp are:
+//
+// • When the default behavior of equality does not suit the needs of the test,
+// custom equality functions can override the equality operation.
+// For example, an equality function may report floats as equal so long as they
+// are within some tolerance of each other.
+//
+// • Types that have an Equal method may use that method to determine equality.
+// This allows package authors to determine the equality operation for the types
+// that they define.
+//
+// • If no custom equality functions are used and no Equal method is defined,
+// equality is determined by recursively comparing the primitive kinds on both
+// values, much like reflect.DeepEqual. Unlike reflect.DeepEqual, unexported
+// fields are not compared by default; they result in panics unless suppressed
+// by using an Ignore option (see cmpopts.IgnoreUnexported) or explicitly compared
+// using the AllowUnexported option.
+package cmp
+
+import (
+	"fmt"
+	"reflect"
+
+	"github.com/google/go-cmp/cmp/internal/diff"
+	"github.com/google/go-cmp/cmp/internal/function"
+	"github.com/google/go-cmp/cmp/internal/value"
+)
+
+// BUG(dsnet): Maps with keys containing NaN values cannot be properly compared due to
+// the reflection package's inability to retrieve such entries. Equal will panic
+// anytime it comes across a NaN key, but this behavior may change.
+//
+// See https://golang.org/issue/11104 for more details.
+
+var nothing = reflect.Value{}
+
+// Equal reports whether x and y are equal by recursively applying the
+// following rules in the given order to x and y and all of their sub-values:
+//
+// • If two values are not of the same type, then they are never equal
+// and the overall result is false.
+//
+// • Let S be the set of all Ignore, Transformer, and Comparer options that
+// remain after applying all path filters, value filters, and type filters.
+// If at least one Ignore exists in S, then the comparison is ignored.
+// If the number of Transformer and Comparer options in S is greater than one,
+// then Equal panics because it is ambiguous which option to use.
+// If S contains a single Transformer, then use that to transform the current
+// values and recursively call Equal on the output values.
+// If S contains a single Comparer, then use that to compare the current values.
+// Otherwise, evaluation proceeds to the next rule.
+//
+// • If the values have an Equal method of the form "(T) Equal(T) bool" or
+// "(T) Equal(I) bool" where T is assignable to I, then use the result of
+// x.Equal(y) even if x or y is nil.
+// Otherwise, no such method exists and evaluation proceeds to the next rule.
+//
+// • Lastly, try to compare x and y based on their basic kinds.
+// Simple kinds like booleans, integers, floats, complex numbers, strings, and
+// channels are compared using the equivalent of the == operator in Go.
+// Functions are only equal if they are both nil, otherwise they are unequal.
+// Pointers are equal if the underlying values they point to are also equal.
+// Interfaces are equal if their underlying concrete values are also equal.
+//
+// Structs are equal if all of their fields are equal. If a struct contains
+// unexported fields, Equal panics unless the AllowUnexported option is used or
+// an Ignore option (e.g., cmpopts.IgnoreUnexported) ignores that field.
+//
+// Arrays, slices, and maps are equal if they are both nil or both non-nil
+// with the same length and the elements at each index or key are equal.
+// Note that a non-nil empty slice and a nil slice are not equal.
+// To equate empty slices and maps, consider using cmpopts.EquateEmpty.
+// Map keys are equal according to the == operator.
+// To use custom comparisons for map keys, consider using cmpopts.SortMaps.
+func Equal(x, y interface{}, opts ...Option) bool {
+	s := newState(opts)
+	s.compareAny(reflect.ValueOf(x), reflect.ValueOf(y))
+	return s.result.Equal()
+}
+
+// Diff returns a human-readable report of the differences between two values.
+// It returns an empty string if and only if Equal returns true for the same
+// input values and options. The output string will use the "-" symbol to
+// indicate elements removed from x, and the "+" symbol to indicate elements
+// added to y.
+//
+// Do not depend on this output being stable.
+func Diff(x, y interface{}, opts ...Option) string {
+	r := new(defaultReporter)
+	opts = Options{Options(opts), r}
+	eq := Equal(x, y, opts...)
+	d := r.String()
+	if (d == "") != eq {
+		panic("inconsistent difference and equality results")
+	}
+	return d
+}
+
+type state struct {
+	// These fields represent the "comparison state".
+	// Calling statelessCompare must not result in observable changes to these.
+	result   diff.Result // The current result of comparison
+	curPath  Path        // The current path in the value tree
+	reporter reporter    // Optional reporter used for difference formatting
+
+	// dynChecker triggers pseudo-random checks for option correctness.
+	// It is safe for statelessCompare to mutate this value.
+	dynChecker dynChecker
+
+	// These fields, once set by processOption, will not change.
+	exporters map[reflect.Type]bool // Set of structs with unexported field visibility
+	opts      Options               // List of all fundamental and filter options
+}
+
+func newState(opts []Option) *state {
+	s := new(state)
+	for _, opt := range opts {
+		s.processOption(opt)
+	}
+	return s
+}
+
+func (s *state) processOption(opt Option) {
+	switch opt := opt.(type) {
+	case nil:
+	case Options:
+		for _, o := range opt {
+			s.processOption(o)
+		}
+	case coreOption:
+		type filtered interface {
+			isFiltered() bool
+		}
+		if fopt, ok := opt.(filtered); ok && !fopt.isFiltered() {
+			panic(fmt.Sprintf("cannot use an unfiltered option: %v", opt))
+		}
+		s.opts = append(s.opts, opt)
+	case visibleStructs:
+		if s.exporters == nil {
+			s.exporters = make(map[reflect.Type]bool)
+		}
+		for t := range opt {
+			s.exporters[t] = true
+		}
+	case reporter:
+		if s.reporter != nil {
+			panic("difference reporter already registered")
+		}
+		s.reporter = opt
+	default:
+		panic(fmt.Sprintf("unknown option %T", opt))
+	}
+}
+
+// statelessCompare compares two values and returns the result.
+// This function is stateless in that it does not alter the current result,
+// or output to any registered reporters.
+func (s *state) statelessCompare(vx, vy reflect.Value) diff.Result {
+	// We do not save and restore the curPath because all of the compareX
+	// methods should properly push and pop from the path.
+	// It is an implementation bug if the contents of curPath differs from
+	// when calling this function to when returning from it.
+
+	oldResult, oldReporter := s.result, s.reporter
+	s.result = diff.Result{} // Reset result
+	s.reporter = nil         // Remove reporter to avoid spurious printouts
+	s.compareAny(vx, vy)
+	res := s.result
+	s.result, s.reporter = oldResult, oldReporter
+	return res
+}
+
+func (s *state) compareAny(vx, vy reflect.Value) {
+	// TODO: Support cyclic data structures.
+
+	// Rule 0: Differing types are never equal.
+	if !vx.IsValid() || !vy.IsValid() {
+		s.report(vx.IsValid() == vy.IsValid(), vx, vy)
+		return
+	}
+	if vx.Type() != vy.Type() {
+		s.report(false, vx, vy) // Possible for path to be empty
+		return
+	}
+	t := vx.Type()
+	if len(s.curPath) == 0 {
+		s.curPath.push(&pathStep{typ: t})
+		defer s.curPath.pop()
+	}
+	vx, vy = s.tryExporting(vx, vy)
+
+	// Rule 1: Check whether an option applies on this node in the value tree.
+	if s.tryOptions(vx, vy, t) {
+		return
+	}
+
+	// Rule 2: Check whether the type has a valid Equal method.
+	if s.tryMethod(vx, vy, t) {
+		return
+	}
+
+	// Rule 3: Recursively descend into each value's underlying kind.
+	switch t.Kind() {
+	case reflect.Bool:
+		s.report(vx.Bool() == vy.Bool(), vx, vy)
+		return
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		s.report(vx.Int() == vy.Int(), vx, vy)
+		return
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
+		s.report(vx.Uint() == vy.Uint(), vx, vy)
+		return
+	case reflect.Float32, reflect.Float64:
+		s.report(vx.Float() == vy.Float(), vx, vy)
+		return
+	case reflect.Complex64, reflect.Complex128:
+		s.report(vx.Complex() == vy.Complex(), vx, vy)
+		return
+	case reflect.String:
+		s.report(vx.String() == vy.String(), vx, vy)
+		return
+	case reflect.Chan, reflect.UnsafePointer:
+		s.report(vx.Pointer() == vy.Pointer(), vx, vy)
+		return
+	case reflect.Func:
+		s.report(vx.IsNil() && vy.IsNil(), vx, vy)
+		return
+	case reflect.Ptr:
+		if vx.IsNil() || vy.IsNil() {
+			s.report(vx.IsNil() && vy.IsNil(), vx, vy)
+			return
+		}
+		s.curPath.push(&indirect{pathStep{t.Elem()}})
+		defer s.curPath.pop()
+		s.compareAny(vx.Elem(), vy.Elem())
+		return
+	case reflect.Interface:
+		if vx.IsNil() || vy.IsNil() {
+			s.report(vx.IsNil() && vy.IsNil(), vx, vy)
+			return
+		}
+		if vx.Elem().Type() != vy.Elem().Type() {
+			s.report(false, vx.Elem(), vy.Elem())
+			return
+		}
+		s.curPath.push(&typeAssertion{pathStep{vx.Elem().Type()}})
+		defer s.curPath.pop()
+		s.compareAny(vx.Elem(), vy.Elem())
+		return
+	case reflect.Slice:
+		if vx.IsNil() || vy.IsNil() {
+			s.report(vx.IsNil() && vy.IsNil(), vx, vy)
+			return
+		}
+		fallthrough
+	case reflect.Array:
+		s.compareArray(vx, vy, t)
+		return
+	case reflect.Map:
+		s.compareMap(vx, vy, t)
+		return
+	case reflect.Struct:
+		s.compareStruct(vx, vy, t)
+		return
+	default:
+		panic(fmt.Sprintf("%v kind not handled", t.Kind()))
+	}
+}
+
+func (s *state) tryExporting(vx, vy reflect.Value) (reflect.Value, reflect.Value) {
+	if sf, ok := s.curPath[len(s.curPath)-1].(*structField); ok && sf.unexported {
+		if sf.force {
+			// Use unsafe pointer arithmetic to get read-write access to an
+			// unexported field in the struct.
+			vx = unsafeRetrieveField(sf.pvx, sf.field)
+			vy = unsafeRetrieveField(sf.pvy, sf.field)
+		} else {
+			// We are not allowed to export the value, so invalidate them
+			// so that tryOptions can panic later if not explicitly ignored.
+			vx = nothing
+			vy = nothing
+		}
+	}
+	return vx, vy
+}
+
+func (s *state) tryOptions(vx, vy reflect.Value, t reflect.Type) bool {
+	// If there were no FilterValues, we will not detect invalid inputs,
+	// so manually check for them and append invalid if necessary.
+	// We still evaluate the options since an ignore can override invalid.
+	opts := s.opts
+	if !vx.IsValid() || !vy.IsValid() {
+		opts = Options{opts, invalid{}}
+	}
+
+	// Evaluate all filters and apply the remaining options.
+	if opt := opts.filter(s, vx, vy, t); opt != nil {
+		opt.apply(s, vx, vy)
+		return true
+	}
+	return false
+}
+
+func (s *state) tryMethod(vx, vy reflect.Value, t reflect.Type) bool {
+	// Check if this type even has an Equal method.
+	m, ok := t.MethodByName("Equal")
+	if !ok || !function.IsType(m.Type, function.EqualAssignable) {
+		return false
+	}
+
+	eq := s.callTTBFunc(m.Func, vx, vy)
+	s.report(eq, vx, vy)
+	return true
+}
+
+func (s *state) callTRFunc(f, v reflect.Value) reflect.Value {
+	v = sanitizeValue(v, f.Type().In(0))
+	if !s.dynChecker.Next() {
+		return f.Call([]reflect.Value{v})[0]
+	}
+
+	// Run the function twice and ensure that we get the same results back.
+	// We run in goroutines so that the race detector (if enabled) can detect
+	// unsafe mutations to the input.
+	c := make(chan reflect.Value)
+	go detectRaces(c, f, v)
+	want := f.Call([]reflect.Value{v})[0]
+	if got := <-c; !s.statelessCompare(got, want).Equal() {
+		// To avoid false-positives with non-reflexive equality operations,
+		// we sanity check whether a value is equal to itself.
+		if !s.statelessCompare(want, want).Equal() {
+			return want
+		}
+		fn := getFuncName(f.Pointer())
+		panic(fmt.Sprintf("non-deterministic function detected: %s", fn))
+	}
+	return want
+}
+
+func (s *state) callTTBFunc(f, x, y reflect.Value) bool {
+	x = sanitizeValue(x, f.Type().In(0))
+	y = sanitizeValue(y, f.Type().In(1))
+	if !s.dynChecker.Next() {
+		return f.Call([]reflect.Value{x, y})[0].Bool()
+	}
+
+	// Swapping the input arguments is sufficient to check that
+	// f is symmetric and deterministic.
+	// We run in goroutines so that the race detector (if enabled) can detect
+	// unsafe mutations to the input.
+	c := make(chan reflect.Value)
+	go detectRaces(c, f, y, x)
+	want := f.Call([]reflect.Value{x, y})[0].Bool()
+	if got := <-c; !got.IsValid() || got.Bool() != want {
+		fn := getFuncName(f.Pointer())
+		panic(fmt.Sprintf("non-deterministic or non-symmetric function detected: %s", fn))
+	}
+	return want
+}
+
+func detectRaces(c chan<- reflect.Value, f reflect.Value, vs ...reflect.Value) {
+	var ret reflect.Value
+	defer func() {
+		recover() // Ignore panics, let the other call to f panic instead
+		c <- ret
+	}()
+	ret = f.Call(vs)[0]
+}
+
+// sanitizeValue converts nil interfaces of type T to those of type R,
+// assuming that T is assignable to R.
+// Otherwise, it returns the input value as is.
+func sanitizeValue(v reflect.Value, t reflect.Type) reflect.Value {
+	// TODO(dsnet): Remove this hacky workaround.
+	// See https://golang.org/issue/22143
+	if v.Kind() == reflect.Interface && v.IsNil() && v.Type() != t {
+		return reflect.New(t).Elem()
+	}
+	return v
+}
+
+func (s *state) compareArray(vx, vy reflect.Value, t reflect.Type) {
+	step := &sliceIndex{pathStep{t.Elem()}, 0, 0}
+	s.curPath.push(step)
+
+	// Compute an edit-script for slices vx and vy.
+	es := diff.Difference(vx.Len(), vy.Len(), func(ix, iy int) diff.Result {
+		step.xkey, step.ykey = ix, iy
+		return s.statelessCompare(vx.Index(ix), vy.Index(iy))
+	})
+
+	// Report the entire slice as is if the arrays are of primitive kind,
+	// and the arrays are different enough.
+	isPrimitive := false
+	switch t.Elem().Kind() {
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
+		reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr,
+		reflect.Bool, reflect.Float32, reflect.Float64, reflect.Complex64, reflect.Complex128:
+		isPrimitive = true
+	}
+	if isPrimitive && es.Dist() > (vx.Len()+vy.Len())/4 {
+		s.curPath.pop() // Pop first since we are reporting the whole slice
+		s.report(false, vx, vy)
+		return
+	}
+
+	// Replay the edit-script.
+	var ix, iy int
+	for _, e := range es {
+		switch e {
+		case diff.UniqueX:
+			step.xkey, step.ykey = ix, -1
+			s.report(false, vx.Index(ix), nothing)
+			ix++
+		case diff.UniqueY:
+			step.xkey, step.ykey = -1, iy
+			s.report(false, nothing, vy.Index(iy))
+			iy++
+		default:
+			step.xkey, step.ykey = ix, iy
+			if e == diff.Identity {
+				s.report(true, vx.Index(ix), vy.Index(iy))
+			} else {
+				s.compareAny(vx.Index(ix), vy.Index(iy))
+			}
+			ix++
+			iy++
+		}
+	}
+	s.curPath.pop()
+	return
+}
+
+func (s *state) compareMap(vx, vy reflect.Value, t reflect.Type) {
+	if vx.IsNil() || vy.IsNil() {
+		s.report(vx.IsNil() && vy.IsNil(), vx, vy)
+		return
+	}
+
+	// We combine and sort the two map keys so that we can perform the
+	// comparisons in a deterministic order.
+	step := &mapIndex{pathStep: pathStep{t.Elem()}}
+	s.curPath.push(step)
+	defer s.curPath.pop()
+	for _, k := range value.SortKeys(append(vx.MapKeys(), vy.MapKeys()...)) {
+		step.key = k
+		vvx := vx.MapIndex(k)
+		vvy := vy.MapIndex(k)
+		switch {
+		case vvx.IsValid() && vvy.IsValid():
+			s.compareAny(vvx, vvy)
+		case vvx.IsValid() && !vvy.IsValid():
+			s.report(false, vvx, nothing)
+		case !vvx.IsValid() && vvy.IsValid():
+			s.report(false, nothing, vvy)
+		default:
+			// It is possible for both vvx and vvy to be invalid if the
+			// key contained a NaN value in it. There is no way in
+			// reflection to be able to retrieve these values.
+			// See https://golang.org/issue/11104
+			panic(fmt.Sprintf("%#v has map key with NaNs", s.curPath))
+		}
+	}
+}
+
+func (s *state) compareStruct(vx, vy reflect.Value, t reflect.Type) {
+	var vax, vay reflect.Value // Addressable versions of vx and vy
+
+	step := &structField{}
+	s.curPath.push(step)
+	defer s.curPath.pop()
+	for i := 0; i < t.NumField(); i++ {
+		vvx := vx.Field(i)
+		vvy := vy.Field(i)
+		step.typ = t.Field(i).Type
+		step.name = t.Field(i).Name
+		step.idx = i
+		step.unexported = !isExported(step.name)
+		if step.unexported {
+			// Defer checking of unexported fields until later to give an
+			// Ignore a chance to ignore the field.
+			if !vax.IsValid() || !vay.IsValid() {
+				// For unsafeRetrieveField to work, the parent struct must
+				// be addressable. Create a new copy of the values if
+				// necessary to make them addressable.
+				vax = makeAddressable(vx)
+				vay = makeAddressable(vy)
+			}
+			step.force = s.exporters[t]
+			step.pvx = vax
+			step.pvy = vay
+			step.field = t.Field(i)
+		}
+		s.compareAny(vvx, vvy)
+	}
+}
+
+// report records the result of a single comparison.
+// It also calls Report if any reporter is registered.
+func (s *state) report(eq bool, vx, vy reflect.Value) {
+	if eq {
+		s.result.NSame++
+	} else {
+		s.result.NDiff++
+	}
+	if s.reporter != nil {
+		s.reporter.Report(vx, vy, eq, s.curPath)
+	}
+}
+
+// dynChecker tracks the state needed to periodically perform checks that
+// user provided functions are symmetric and deterministic.
+// The zero value is safe for immediate use.
+type dynChecker struct{ curr, next int }
+
+// Next increments the state and reports whether a check should be performed.
+//
+// Checks occur every Nth function call, where N is a triangular number:
+//	0 1 3 6 10 15 21 28 36 45 55 66 78 91 105 120 136 153 171 190 ...
+// See https://en.wikipedia.org/wiki/Triangular_number
+//
+// This sequence ensures that the cost of checks drops significantly as
+// the number of functions calls grows larger.
+func (dc *dynChecker) Next() bool {
+	ok := dc.curr == dc.next
+	if ok {
+		dc.curr = 0
+		dc.next++
+	}
+	dc.curr++
+	return ok
+}
+
+// makeAddressable returns a value that is always addressable.
+// It returns the input verbatim if it is already addressable,
+// otherwise it creates a new value and returns an addressable copy.
+func makeAddressable(v reflect.Value) reflect.Value {
+	if v.CanAddr() {
+		return v
+	}
+	vc := reflect.New(v.Type()).Elem()
+	vc.Set(v)
+	return vc
+}
diff --git a/vendor/github.com/google/go-cmp/cmp/internal/diff/debug_disable.go b/vendor/github.com/google/go-cmp/cmp/internal/diff/debug_disable.go
new file mode 100644
index 00000000..42afa496
--- /dev/null
+++ b/vendor/github.com/google/go-cmp/cmp/internal/diff/debug_disable.go
@@ -0,0 +1,17 @@
+// Copyright 2017, The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE.md file.
+
+// +build !debug
+
+package diff
+
+var debug debugger
+
+type debugger struct{}
+
+func (debugger) Begin(_, _ int, f EqualFunc, _, _ *EditScript) EqualFunc {
+	return f
+}
+func (debugger) Update() {}
+func (debugger) Finish() {}
diff --git a/vendor/github.com/google/go-cmp/cmp/internal/diff/debug_enable.go b/vendor/github.com/google/go-cmp/cmp/internal/diff/debug_enable.go
new file mode 100644
index 00000000..fd9f7f17
--- /dev/null
+++ b/vendor/github.com/google/go-cmp/cmp/internal/diff/debug_enable.go
@@ -0,0 +1,122 @@
+// Copyright 2017, The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE.md file.
+
+// +build debug
+
+package diff
+
+import (
+	"fmt"
+	"strings"
+	"sync"
+	"time"
+)
+
+// The algorithm can be seen running in real-time by enabling debugging:
+//	go test -tags=debug -v
+//
+// Example output:
+//	=== RUN   TestDifference/#34
+//	┌───────────────────────────────┐
+//	│ \ · · · · · · · · · · · · · · │
+//	│ · # · · · · · · · · · · · · · │
+//	│ · \ · · · · · · · · · · · · · │
+//	│ · · \ · · · · · · · · · · · · │
+//	│ · · · X # · · · · · · · · · · │
+//	│ · · · # \ · · · · · · · · · · │
+//	│ · · · · · # # · · · · · · · · │
+//	│ · · · · · # \ · · · · · · · · │
+//	│ · · · · · · · \ · · · · · · · │
+//	│ · · · · · · · · \ · · · · · · │
+//	│ · · · · · · · · · \ · · · · · │
+//	│ · · · · · · · · · · \ · · # · │
+//	│ · · · · · · · · · · · \ # # · │
+//	│ · · · · · · · · · · · # # # · │
+//	│ · · · · · · · · · · # # # # · │
+//	│ · · · · · · · · · # # # # # · │
+//	│ · · · · · · · · · · · · · · \ │
+//	└───────────────────────────────┘
+//	[.Y..M.XY......YXYXY.|]
+//
+// The grid represents the edit-graph where the horizontal axis represents
+// list X and the vertical axis represents list Y. The start of the two lists
+// is the top-left, while the ends are the bottom-right. The '·' represents
+// an unexplored node in the graph. The '\' indicates that the two symbols
+// from list X and Y are equal. The 'X' indicates that two symbols are similar
+// (but not exactly equal) to each other. The '#' indicates that the two symbols
+// are different (and not similar). The algorithm traverses this graph trying to
+// make the paths starting in the top-left and the bottom-right connect.
+//
+// The series of '.', 'X', 'Y', and 'M' characters at the bottom represents
+// the currently established path from the forward and reverse searches,
+// separated by a '|' character.
+
+const (
+	updateDelay  = 100 * time.Millisecond
+	finishDelay  = 500 * time.Millisecond
+	ansiTerminal = true // ANSI escape codes used to move terminal cursor
+)
+
+var debug debugger
+
+type debugger struct {
+	sync.Mutex
+	p1, p2           EditScript
+	fwdPath, revPath *EditScript
+	grid             []byte
+	lines            int
+}
+
+func (dbg *debugger) Begin(nx, ny int, f EqualFunc, p1, p2 *EditScript) EqualFunc {
+	dbg.Lock()
+	dbg.fwdPath, dbg.revPath = p1, p2
+	top := "┌─" + strings.Repeat("──", nx) + "┐\n"
+	row := "│ " + strings.Repeat("· ", nx) + "│\n"
+	btm := "└─" + strings.Repeat("──", nx) + "┘\n"
+	dbg.grid = []byte(top + strings.Repeat(row, ny) + btm)
+	dbg.lines = strings.Count(dbg.String(), "\n")
+	fmt.Print(dbg)
+
+	// Wrap the EqualFunc so that we can intercept each result.
+	return func(ix, iy int) (r Result) {
+		cell := dbg.grid[len(top)+iy*len(row):][len("│ ")+len("· ")*ix:][:len("·")]
+		for i := range cell {
+			cell[i] = 0 // Zero out the multiple bytes of UTF-8 middle-dot
+		}
+		switch r = f(ix, iy); {
+		case r.Equal():
+			cell[0] = '\\'
+		case r.Similar():
+			cell[0] = 'X'
+		default:
+			cell[0] = '#'
+		}
+		return
+	}
+}
+
+func (dbg *debugger) Update() {
+	dbg.print(updateDelay)
+}
+
+func (dbg *debugger) Finish() {
+	dbg.print(finishDelay)
+	dbg.Unlock()
+}
+
+func (dbg *debugger) String() string {
+	dbg.p1, dbg.p2 = *dbg.fwdPath, dbg.p2[:0]
+	for i := len(*dbg.revPath) - 1; i >= 0; i-- {
+		dbg.p2 = append(dbg.p2, (*dbg.revPath)[i])
+	}
+	return fmt.Sprintf("%s[%v|%v]\n\n", dbg.grid, dbg.p1, dbg.p2)
+}
+
+func (dbg *debugger) print(d time.Duration) {
+	if ansiTerminal {
+		fmt.Printf("\x1b[%dA", dbg.lines) // Reset terminal cursor
+	}
+	fmt.Print(dbg)
+	time.Sleep(d)
+}
diff --git a/vendor/github.com/google/go-cmp/cmp/internal/diff/diff.go b/vendor/github.com/google/go-cmp/cmp/internal/diff/diff.go
new file mode 100644
index 00000000..260befea
--- /dev/null
+++ b/vendor/github.com/google/go-cmp/cmp/internal/diff/diff.go
@@ -0,0 +1,363 @@
+// Copyright 2017, The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE.md file.
+
+// Package diff implements an algorithm for producing edit-scripts.
+// The edit-script is a sequence of operations needed to transform one list
+// of symbols into another (or vice-versa). The edits allowed are insertions,
+// deletions, and modifications. The summation of all edits is called the
+// Levenshtein distance as this problem is well-known in computer science.
+//
+// This package prioritizes performance over accuracy. That is, the run time
+// is more important than obtaining a minimal Levenshtein distance.
+package diff
+
+// EditType represents a single operation within an edit-script.
+type EditType uint8
+
+const (
+	// Identity indicates that a symbol pair is identical in both list X and Y.
+	Identity EditType = iota
+	// UniqueX indicates that a symbol only exists in X and not Y.
+	UniqueX
+	// UniqueY indicates that a symbol only exists in Y and not X.
+	UniqueY
+	// Modified indicates that a symbol pair is a modification of each other.
+	Modified
+)
+
+// EditScript represents the series of differences between two lists.
+type EditScript []EditType
+
+// String returns a human-readable string representing the edit-script where
+// Identity, UniqueX, UniqueY, and Modified are represented by the
+// '.', 'X', 'Y', and 'M' characters, respectively.
+func (es EditScript) String() string {
+	b := make([]byte, len(es))
+	for i, e := range es {
+		switch e {
+		case Identity:
+			b[i] = '.'
+		case UniqueX:
+			b[i] = 'X'
+		case UniqueY:
+			b[i] = 'Y'
+		case Modified:
+			b[i] = 'M'
+		default:
+			panic("invalid edit-type")
+		}
+	}
+	return string(b)
+}
+
+// stats returns a histogram of the number of each type of edit operation.
+func (es EditScript) stats() (s struct{ NI, NX, NY, NM int }) {
+	for _, e := range es {
+		switch e {
+		case Identity:
+			s.NI++
+		case UniqueX:
+			s.NX++
+		case UniqueY:
+			s.NY++
+		case Modified:
+			s.NM++
+		default:
+			panic("invalid edit-type")
+		}
+	}
+	return
+}
+
+// Dist is the Levenshtein distance and is guaranteed to be 0 if and only if
+// lists X and Y are equal.
+func (es EditScript) Dist() int { return len(es) - es.stats().NI }
+
+// LenX is the length of the X list.
+func (es EditScript) LenX() int { return len(es) - es.stats().NY }
+
+// LenY is the length of the Y list.
+func (es EditScript) LenY() int { return len(es) - es.stats().NX }
+
+// EqualFunc reports whether the symbols at indexes ix and iy are equal.
+// When called by Difference, the index is guaranteed to be within nx and ny.
+type EqualFunc func(ix int, iy int) Result
+
+// Result is the result of comparison.
+// NSame is the number of sub-elements that are equal.
+// NDiff is the number of sub-elements that are not equal.
+type Result struct{ NSame, NDiff int }
+
+// Equal indicates whether the symbols are equal. Two symbols are equal
+// if and only if NDiff == 0. If Equal, then they are also Similar.
+func (r Result) Equal() bool { return r.NDiff == 0 }
+
+// Similar indicates whether two symbols are similar and may be represented
+// by using the Modified type. As a special case, we consider binary comparisons
+// (i.e., those that return Result{1, 0} or Result{0, 1}) to be similar.
+//
+// The exact ratio of NSame to NDiff to determine similarity may change.
+func (r Result) Similar() bool {
+	// Use NSame+1 to offset NSame so that binary comparisons are similar.
+	return r.NSame+1 >= r.NDiff
+}
+
+// Difference reports whether two lists of lengths nx and ny are equal
+// given the definition of equality provided as f.
+//
+// This function returns an edit-script, which is a sequence of operations
+// needed to convert one list into the other. The following invariants for
+// the edit-script are maintained:
+//	• eq == (es.Dist()==0)
+//	• nx == es.LenX()
+//	• ny == es.LenY()
+//
+// This algorithm is not guaranteed to be an optimal solution (i.e., one that
+// produces an edit-script with a minimal Levenshtein distance). This algorithm
+// favors performance over optimality. The exact output is not guaranteed to
+// be stable and may change over time.
+func Difference(nx, ny int, f EqualFunc) (es EditScript) {
+	// This algorithm is based on traversing what is known as an "edit-graph".
+	// See Figure 1 from "An O(ND) Difference Algorithm and Its Variations"
+	// by Eugene W. Myers. Since D can be as large as N itself, this is
+	// effectively O(N^2). Unlike the algorithm from that paper, we are not
+	// interested in the optimal path, but at least some "decent" path.
+	//
+	// For example, let X and Y be lists of symbols:
+	//	X = [A B C A B B A]
+	//	Y = [C B A B A C]
+	//
+	// The edit-graph can be drawn as the following:
+	//	   A B C A B B A
+	//	  ┌─────────────┐
+	//	C │_|_|\|_|_|_|_│ 0
+	//	B │_|\|_|_|\|\|_│ 1
+	//	A │\|_|_|\|_|_|\│ 2
+	//	B │_|\|_|_|\|\|_│ 3
+	//	A │\|_|_|\|_|_|\│ 4
+	//	C │ | |\| | | | │ 5
+	//	  └─────────────┘ 6
+	//	   0 1 2 3 4 5 6 7
+	//
+	// List X is written along the horizontal axis, while list Y is written
+	// along the vertical axis. At any point on this grid, if the symbol in
+	// list X matches the corresponding symbol in list Y, then a '\' is drawn.
+	// The goal of any minimal edit-script algorithm is to find a path from the
+	// top-left corner to the bottom-right corner, while traveling through the
+	// fewest horizontal or vertical edges.
+	// A horizontal edge is equivalent to inserting a symbol from list X.
+	// A vertical edge is equivalent to inserting a symbol from list Y.
+	// A diagonal edge is equivalent to a matching symbol between both X and Y.
+
+	// Invariants:
+	//	• 0 ≤ fwdPath.X ≤ (fwdFrontier.X, revFrontier.X) ≤ revPath.X ≤ nx
+	//	• 0 ≤ fwdPath.Y ≤ (fwdFrontier.Y, revFrontier.Y) ≤ revPath.Y ≤ ny
+	//
+	// In general:
+	//	• fwdFrontier.X < revFrontier.X
+	//	• fwdFrontier.Y < revFrontier.Y
+	// Unless, it is time for the algorithm to terminate.
+	fwdPath := path{+1, point{0, 0}, make(EditScript, 0, (nx+ny)/2)}
+	revPath := path{-1, point{nx, ny}, make(EditScript, 0)}
+	fwdFrontier := fwdPath.point // Forward search frontier
+	revFrontier := revPath.point // Reverse search frontier
+
+	// Search budget bounds the cost of searching for better paths.
+	// The longest sequence of non-matching symbols that can be tolerated is
+	// approximately the square-root of the search budget.
+	searchBudget := 4 * (nx + ny) // O(n)
+
+	// The algorithm below is a greedy, meet-in-the-middle algorithm for
+	// computing sub-optimal edit-scripts between two lists.
+	//
+	// The algorithm is approximately as follows:
+	//	• Searching for differences switches back-and-forth between
+	//	a search that starts at the beginning (the top-left corner), and
+	//	a search that starts at the end (the bottom-right corner). The goal of
+	//	the search is connect with the search from the opposite corner.
+	//	• As we search, we build a path in a greedy manner, where the first
+	//	match seen is added to the path (this is sub-optimal, but provides a
+	//	decent result in practice). When matches are found, we try the next pair
+	//	of symbols in the lists and follow all matches as far as possible.
+	//	• When searching for matches, we search along a diagonal going through
+	//	through the "frontier" point. If no matches are found, we advance the
+	//	frontier towards the opposite corner.
+	//	• This algorithm terminates when either the X coordinates or the
+	//	Y coordinates of the forward and reverse frontier points ever intersect.
+	//
+	// This algorithm is correct even if searching only in the forward direction
+	// or in the reverse direction. We do both because it is commonly observed
+	// that two lists commonly differ because elements were added to the front
+	// or end of the other list.
+	//
+	// Running the tests with the "debug" build tag prints a visualization of
+	// the algorithm running in real-time. This is educational for understanding
+	// how the algorithm works. See debug_enable.go.
+	f = debug.Begin(nx, ny, f, &fwdPath.es, &revPath.es)
+	for {
+		// Forward search from the beginning.
+		if fwdFrontier.X >= revFrontier.X || fwdFrontier.Y >= revFrontier.Y || searchBudget == 0 {
+			break
+		}
+		for stop1, stop2, i := false, false, 0; !(stop1 && stop2) && searchBudget > 0; i++ {
+			// Search in a diagonal pattern for a match.
+			z := zigzag(i)
+			p := point{fwdFrontier.X + z, fwdFrontier.Y - z}
+			switch {
+			case p.X >= revPath.X || p.Y < fwdPath.Y:
+				stop1 = true // Hit top-right corner
+			case p.Y >= revPath.Y || p.X < fwdPath.X:
+				stop2 = true // Hit bottom-left corner
+			case f(p.X, p.Y).Equal():
+				// Match found, so connect the path to this point.
+				fwdPath.connect(p, f)
+				fwdPath.append(Identity)
+				// Follow sequence of matches as far as possible.
+				for fwdPath.X < revPath.X && fwdPath.Y < revPath.Y {
+					if !f(fwdPath.X, fwdPath.Y).Equal() {
+						break
+					}
+					fwdPath.append(Identity)
+				}
+				fwdFrontier = fwdPath.point
+				stop1, stop2 = true, true
+			default:
+				searchBudget-- // Match not found
+			}
+			debug.Update()
+		}
+		// Advance the frontier towards reverse point.
+		if revPath.X-fwdFrontier.X >= revPath.Y-fwdFrontier.Y {
+			fwdFrontier.X++
+		} else {
+			fwdFrontier.Y++
+		}
+
+		// Reverse search from the end.
+		if fwdFrontier.X >= revFrontier.X || fwdFrontier.Y >= revFrontier.Y || searchBudget == 0 {
+			break
+		}
+		for stop1, stop2, i := false, false, 0; !(stop1 && stop2) && searchBudget > 0; i++ {
+			// Search in a diagonal pattern for a match.
+			z := zigzag(i)
+			p := point{revFrontier.X - z, revFrontier.Y + z}
+			switch {
+			case fwdPath.X >= p.X || revPath.Y < p.Y:
+				stop1 = true // Hit bottom-left corner
+			case fwdPath.Y >= p.Y || revPath.X < p.X:
+				stop2 = true // Hit top-right corner
+			case f(p.X-1, p.Y-1).Equal():
+				// Match found, so connect the path to this point.
+				revPath.connect(p, f)
+				revPath.append(Identity)
+				// Follow sequence of matches as far as possible.
+				for fwdPath.X < revPath.X && fwdPath.Y < revPath.Y {
+					if !f(revPath.X-1, revPath.Y-1).Equal() {
+						break
+					}
+					revPath.append(Identity)
+				}
+				revFrontier = revPath.point
+				stop1, stop2 = true, true
+			default:
+				searchBudget-- // Match not found
+			}
+			debug.Update()
+		}
+		// Advance the frontier towards forward point.
+		if revFrontier.X-fwdPath.X >= revFrontier.Y-fwdPath.Y {
+			revFrontier.X--
+		} else {
+			revFrontier.Y--
+		}
+	}
+
+	// Join the forward and reverse paths and then append the reverse path.
+	fwdPath.connect(revPath.point, f)
+	for i := len(revPath.es) - 1; i >= 0; i-- {
+		t := revPath.es[i]
+		revPath.es = revPath.es[:i]
+		fwdPath.append(t)
+	}
+	debug.Finish()
+	return fwdPath.es
+}
+
+type path struct {
+	dir   int // +1 if forward, -1 if reverse
+	point     // Leading point of the EditScript path
+	es    EditScript
+}
+
+// connect appends any necessary Identity, Modified, UniqueX, or UniqueY types
+// to the edit-script to connect p.point to dst.
+func (p *path) connect(dst point, f EqualFunc) {
+	if p.dir > 0 {
+		// Connect in forward direction.
+		for dst.X > p.X && dst.Y > p.Y {
+			switch r := f(p.X, p.Y); {
+			case r.Equal():
+				p.append(Identity)
+			case r.Similar():
+				p.append(Modified)
+			case dst.X-p.X >= dst.Y-p.Y:
+				p.append(UniqueX)
+			default:
+				p.append(UniqueY)
+			}
+		}
+		for dst.X > p.X {
+			p.append(UniqueX)
+		}
+		for dst.Y > p.Y {
+			p.append(UniqueY)
+		}
+	} else {
+		// Connect in reverse direction.
+		for p.X > dst.X && p.Y > dst.Y {
+			switch r := f(p.X-1, p.Y-1); {
+			case r.Equal():
+				p.append(Identity)
+			case r.Similar():
+				p.append(Modified)
+			case p.Y-dst.Y >= p.X-dst.X:
+				p.append(UniqueY)
+			default:
+				p.append(UniqueX)
+			}
+		}
+		for p.X > dst.X {
+			p.append(UniqueX)
+		}
+		for p.Y > dst.Y {
+			p.append(UniqueY)
+		}
+	}
+}
+
+func (p *path) append(t EditType) {
+	p.es = append(p.es, t)
+	switch t {
+	case Identity, Modified:
+		p.add(p.dir, p.dir)
+	case UniqueX:
+		p.add(p.dir, 0)
+	case UniqueY:
+		p.add(0, p.dir)
+	}
+	debug.Update()
+}
+
+type point struct{ X, Y int }
+
+func (p *point) add(dx, dy int) { p.X += dx; p.Y += dy }
+
+// zigzag maps a consecutive sequence of integers to a zig-zag sequence.
+//	[0 1 2 3 4 5 ...] => [0 -1 +1 -2 +2 ...]
+func zigzag(x int) int {
+	if x&1 != 0 {
+		x = ^x
+	}
+	return x >> 1
+}
diff --git a/vendor/github.com/google/go-cmp/cmp/internal/function/func.go b/vendor/github.com/google/go-cmp/cmp/internal/function/func.go
new file mode 100644
index 00000000..4c35ff11
--- /dev/null
+++ b/vendor/github.com/google/go-cmp/cmp/internal/function/func.go
@@ -0,0 +1,49 @@
+// Copyright 2017, The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE.md file.
+
+// Package function identifies function types.
+package function
+
+import "reflect"
+
+type funcType int
+
+const (
+	_ funcType = iota
+
+	ttbFunc // func(T, T) bool
+	tibFunc // func(T, I) bool
+	trFunc  // func(T) R
+
+	Equal           = ttbFunc // func(T, T) bool
+	EqualAssignable = tibFunc // func(T, I) bool; encapsulates func(T, T) bool
+	Transformer     = trFunc  // func(T) R
+	ValueFilter     = ttbFunc // func(T, T) bool
+	Less            = ttbFunc // func(T, T) bool
+)
+
+var boolType = reflect.TypeOf(true)
+
+// IsType reports whether the reflect.Type is of the specified function type.
+func IsType(t reflect.Type, ft funcType) bool {
+	if t == nil || t.Kind() != reflect.Func || t.IsVariadic() {
+		return false
+	}
+	ni, no := t.NumIn(), t.NumOut()
+	switch ft {
+	case ttbFunc: // func(T, T) bool
+		if ni == 2 && no == 1 && t.In(0) == t.In(1) && t.Out(0) == boolType {
+			return true
+		}
+	case tibFunc: // func(T, I) bool
+		if ni == 2 && no == 1 && t.In(0).AssignableTo(t.In(1)) && t.Out(0) == boolType {
+			return true
+		}
+	case trFunc: // func(T) R
+		if ni == 1 && no == 1 {
+			return true
+		}
+	}
+	return false
+}
diff --git a/vendor/github.com/google/go-cmp/cmp/internal/value/format.go b/vendor/github.com/google/go-cmp/cmp/internal/value/format.go
new file mode 100644
index 00000000..657e5087
--- /dev/null
+++ b/vendor/github.com/google/go-cmp/cmp/internal/value/format.go
@@ -0,0 +1,277 @@
+// Copyright 2017, The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE.md file.
+
+// Package value provides functionality for reflect.Value types.
+package value
+
+import (
+	"fmt"
+	"reflect"
+	"strconv"
+	"strings"
+	"unicode"
+)
+
+var stringerIface = reflect.TypeOf((*fmt.Stringer)(nil)).Elem()
+
+// Format formats the value v as a string.
+//
+// This is similar to fmt.Sprintf("%+v", v) except this:
+//	* Prints the type unless it can be elided
+//	* Avoids printing struct fields that are zero
+//	* Prints a nil-slice as being nil, not empty
+//	* Prints map entries in deterministic order
+func Format(v reflect.Value, conf FormatConfig) string {
+	conf.printType = true
+	conf.followPointers = true
+	conf.realPointers = true
+	return formatAny(v, conf, nil)
+}
+
+type FormatConfig struct {
+	UseStringer        bool // Should the String method be used if available?
+	printType          bool // Should we print the type before the value?
+	PrintPrimitiveType bool // Should we print the type of primitives?
+	followPointers     bool // Should we recursively follow pointers?
+	realPointers       bool // Should we print the real address of pointers?
+}
+
+func formatAny(v reflect.Value, conf FormatConfig, visited map[uintptr]bool) string {
+	// TODO: Should this be a multi-line printout in certain situations?
+
+	if !v.IsValid() {
+		return "<non-existent>"
+	}
+	if conf.UseStringer && v.Type().Implements(stringerIface) && v.CanInterface() {
+		if (v.Kind() == reflect.Ptr || v.Kind() == reflect.Interface) && v.IsNil() {
+			return "<nil>"
+		}
+
+		const stringerPrefix = "s" // Indicates that the String method was used
+		s := v.Interface().(fmt.Stringer).String()
+		return stringerPrefix + formatString(s)
+	}
+
+	switch v.Kind() {
+	case reflect.Bool:
+		return formatPrimitive(v.Type(), v.Bool(), conf)
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		return formatPrimitive(v.Type(), v.Int(), conf)
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
+		if v.Type().PkgPath() == "" || v.Kind() == reflect.Uintptr {
+			// Unnamed uints are usually bytes or words, so use hexadecimal.
+			return formatPrimitive(v.Type(), formatHex(v.Uint()), conf)
+		}
+		return formatPrimitive(v.Type(), v.Uint(), conf)
+	case reflect.Float32, reflect.Float64:
+		return formatPrimitive(v.Type(), v.Float(), conf)
+	case reflect.Complex64, reflect.Complex128:
+		return formatPrimitive(v.Type(), v.Complex(), conf)
+	case reflect.String:
+		return formatPrimitive(v.Type(), formatString(v.String()), conf)
+	case reflect.UnsafePointer, reflect.Chan, reflect.Func:
+		return formatPointer(v, conf)
+	case reflect.Ptr:
+		if v.IsNil() {
+			if conf.printType {
+				return fmt.Sprintf("(%v)(nil)", v.Type())
+			}
+			return "<nil>"
+		}
+		if visited[v.Pointer()] || !conf.followPointers {
+			return formatPointer(v, conf)
+		}
+		visited = insertPointer(visited, v.Pointer())
+		return "&" + formatAny(v.Elem(), conf, visited)
+	case reflect.Interface:
+		if v.IsNil() {
+			if conf.printType {
+				return fmt.Sprintf("%v(nil)", v.Type())
+			}
+			return "<nil>"
+		}
+		return formatAny(v.Elem(), conf, visited)
+	case reflect.Slice:
+		if v.IsNil() {
+			if conf.printType {
+				return fmt.Sprintf("%v(nil)", v.Type())
+			}
+			return "<nil>"
+		}
+		if visited[v.Pointer()] {
+			return formatPointer(v, conf)
+		}
+		visited = insertPointer(visited, v.Pointer())
+		fallthrough
+	case reflect.Array:
+		var ss []string
+		subConf := conf
+		subConf.printType = v.Type().Elem().Kind() == reflect.Interface
+		for i := 0; i < v.Len(); i++ {
+			s := formatAny(v.Index(i), subConf, visited)
+			ss = append(ss, s)
+		}
+		s := fmt.Sprintf("{%s}", strings.Join(ss, ", "))
+		if conf.printType {
+			return v.Type().String() + s
+		}
+		return s
+	case reflect.Map:
+		if v.IsNil() {
+			if conf.printType {
+				return fmt.Sprintf("%v(nil)", v.Type())
+			}
+			return "<nil>"
+		}
+		if visited[v.Pointer()] {
+			return formatPointer(v, conf)
+		}
+		visited = insertPointer(visited, v.Pointer())
+
+		var ss []string
+		keyConf, valConf := conf, conf
+		keyConf.printType = v.Type().Key().Kind() == reflect.Interface
+		keyConf.followPointers = false
+		valConf.printType = v.Type().Elem().Kind() == reflect.Interface
+		for _, k := range SortKeys(v.MapKeys()) {
+			sk := formatAny(k, keyConf, visited)
+			sv := formatAny(v.MapIndex(k), valConf, visited)
+			ss = append(ss, fmt.Sprintf("%s: %s", sk, sv))
+		}
+		s := fmt.Sprintf("{%s}", strings.Join(ss, ", "))
+		if conf.printType {
+			return v.Type().String() + s
+		}
+		return s
+	case reflect.Struct:
+		var ss []string
+		subConf := conf
+		subConf.printType = true
+		for i := 0; i < v.NumField(); i++ {
+			vv := v.Field(i)
+			if isZero(vv) {
+				continue // Elide zero value fields
+			}
+			name := v.Type().Field(i).Name
+			subConf.UseStringer = conf.UseStringer
+			s := formatAny(vv, subConf, visited)
+			ss = append(ss, fmt.Sprintf("%s: %s", name, s))
+		}
+		s := fmt.Sprintf("{%s}", strings.Join(ss, ", "))
+		if conf.printType {
+			return v.Type().String() + s
+		}
+		return s
+	default:
+		panic(fmt.Sprintf("%v kind not handled", v.Kind()))
+	}
+}
+
+func formatString(s string) string {
+	// Use quoted string if it the same length as a raw string literal.
+	// Otherwise, attempt to use the raw string form.
+	qs := strconv.Quote(s)
+	if len(qs) == 1+len(s)+1 {
+		return qs
+	}
+
+	// Disallow newlines to ensure output is a single line.
+	// Only allow printable runes for readability purposes.
+	rawInvalid := func(r rune) bool {
+		return r == '`' || r == '\n' || !unicode.IsPrint(r)
+	}
+	if strings.IndexFunc(s, rawInvalid) < 0 {
+		return "`" + s + "`"
+	}
+	return qs
+}
+
+func formatPrimitive(t reflect.Type, v interface{}, conf FormatConfig) string {
+	if conf.printType && (conf.PrintPrimitiveType || t.PkgPath() != "") {
+		return fmt.Sprintf("%v(%v)", t, v)
+	}
+	return fmt.Sprintf("%v", v)
+}
+
+func formatPointer(v reflect.Value, conf FormatConfig) string {
+	p := v.Pointer()
+	if !conf.realPointers {
+		p = 0 // For deterministic printing purposes
+	}
+	s := formatHex(uint64(p))
+	if conf.printType {
+		return fmt.Sprintf("(%v)(%s)", v.Type(), s)
+	}
+	return s
+}
+
+func formatHex(u uint64) string {
+	var f string
+	switch {
+	case u <= 0xff:
+		f = "0x%02x"
+	case u <= 0xffff:
+		f = "0x%04x"
+	case u <= 0xffffff:
+		f = "0x%06x"
+	case u <= 0xffffffff:
+		f = "0x%08x"
+	case u <= 0xffffffffff:
+		f = "0x%010x"
+	case u <= 0xffffffffffff:
+		f = "0x%012x"
+	case u <= 0xffffffffffffff:
+		f = "0x%014x"
+	case u <= 0xffffffffffffffff:
+		f = "0x%016x"
+	}
+	return fmt.Sprintf(f, u)
+}
+
+// insertPointer insert p into m, allocating m if necessary.
+func insertPointer(m map[uintptr]bool, p uintptr) map[uintptr]bool {
+	if m == nil {
+		m = make(map[uintptr]bool)
+	}
+	m[p] = true
+	return m
+}
+
+// isZero reports whether v is the zero value.
+// This does not rely on Interface and so can be used on unexported fields.
+func isZero(v reflect.Value) bool {
+	switch v.Kind() {
+	case reflect.Bool:
+		return v.Bool() == false
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		return v.Int() == 0
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
+		return v.Uint() == 0
+	case reflect.Float32, reflect.Float64:
+		return v.Float() == 0
+	case reflect.Complex64, reflect.Complex128:
+		return v.Complex() == 0
+	case reflect.String:
+		return v.String() == ""
+	case reflect.UnsafePointer:
+		return v.Pointer() == 0
+	case reflect.Chan, reflect.Func, reflect.Interface, reflect.Ptr, reflect.Map, reflect.Slice:
+		return v.IsNil()
+	case reflect.Array:
+		for i := 0; i < v.Len(); i++ {
+			if !isZero(v.Index(i)) {
+				return false
+			}
+		}
+		return true
+	case reflect.Struct:
+		for i := 0; i < v.NumField(); i++ {
+			if !isZero(v.Field(i)) {
+				return false
+			}
+		}
+		return true
+	}
+	return false
+}
diff --git a/vendor/github.com/google/go-cmp/cmp/internal/value/sort.go b/vendor/github.com/google/go-cmp/cmp/internal/value/sort.go
new file mode 100644
index 00000000..fe8aa27a
--- /dev/null
+++ b/vendor/github.com/google/go-cmp/cmp/internal/value/sort.go
@@ -0,0 +1,111 @@
+// Copyright 2017, The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE.md file.
+
+package value
+
+import (
+	"fmt"
+	"math"
+	"reflect"
+	"sort"
+)
+
+// SortKeys sorts a list of map keys, deduplicating keys if necessary.
+// The type of each value must be comparable.
+func SortKeys(vs []reflect.Value) []reflect.Value {
+	if len(vs) == 0 {
+		return vs
+	}
+
+	// Sort the map keys.
+	sort.Sort(valueSorter(vs))
+
+	// Deduplicate keys (fails for NaNs).
+	vs2 := vs[:1]
+	for _, v := range vs[1:] {
+		if isLess(vs2[len(vs2)-1], v) {
+			vs2 = append(vs2, v)
+		}
+	}
+	return vs2
+}
+
+// TODO: Use sort.Slice once Google AppEngine is on Go1.8 or above.
+type valueSorter []reflect.Value
+
+func (vs valueSorter) Len() int           { return len(vs) }
+func (vs valueSorter) Less(i, j int) bool { return isLess(vs[i], vs[j]) }
+func (vs valueSorter) Swap(i, j int)      { vs[i], vs[j] = vs[j], vs[i] }
+
+// isLess is a generic function for sorting arbitrary map keys.
+// The inputs must be of the same type and must be comparable.
+func isLess(x, y reflect.Value) bool {
+	switch x.Type().Kind() {
+	case reflect.Bool:
+		return !x.Bool() && y.Bool()
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		return x.Int() < y.Int()
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
+		return x.Uint() < y.Uint()
+	case reflect.Float32, reflect.Float64:
+		fx, fy := x.Float(), y.Float()
+		return fx < fy || math.IsNaN(fx) && !math.IsNaN(fy)
+	case reflect.Complex64, reflect.Complex128:
+		cx, cy := x.Complex(), y.Complex()
+		rx, ix, ry, iy := real(cx), imag(cx), real(cy), imag(cy)
+		if rx == ry || (math.IsNaN(rx) && math.IsNaN(ry)) {
+			return ix < iy || math.IsNaN(ix) && !math.IsNaN(iy)
+		}
+		return rx < ry || math.IsNaN(rx) && !math.IsNaN(ry)
+	case reflect.Ptr, reflect.UnsafePointer, reflect.Chan:
+		return x.Pointer() < y.Pointer()
+	case reflect.String:
+		return x.String() < y.String()
+	case reflect.Array:
+		for i := 0; i < x.Len(); i++ {
+			if isLess(x.Index(i), y.Index(i)) {
+				return true
+			}
+			if isLess(y.Index(i), x.Index(i)) {
+				return false
+			}
+		}
+		return false
+	case reflect.Struct:
+		for i := 0; i < x.NumField(); i++ {
+			if isLess(x.Field(i), y.Field(i)) {
+				return true
+			}
+			if isLess(y.Field(i), x.Field(i)) {
+				return false
+			}
+		}
+		return false
+	case reflect.Interface:
+		vx, vy := x.Elem(), y.Elem()
+		if !vx.IsValid() || !vy.IsValid() {
+			return !vx.IsValid() && vy.IsValid()
+		}
+		tx, ty := vx.Type(), vy.Type()
+		if tx == ty {
+			return isLess(x.Elem(), y.Elem())
+		}
+		if tx.Kind() != ty.Kind() {
+			return vx.Kind() < vy.Kind()
+		}
+		if tx.String() != ty.String() {
+			return tx.String() < ty.String()
+		}
+		if tx.PkgPath() != ty.PkgPath() {
+			return tx.PkgPath() < ty.PkgPath()
+		}
+		// This can happen in rare situations, so we fallback to just comparing
+		// the unique pointer for a reflect.Type. This guarantees deterministic
+		// ordering within a program, but it is obviously not stable.
+		return reflect.ValueOf(vx.Type()).Pointer() < reflect.ValueOf(vy.Type()).Pointer()
+	default:
+		// Must be Func, Map, or Slice; which are not comparable.
+		panic(fmt.Sprintf("%T is not comparable", x.Type()))
+	}
+}
diff --git a/vendor/github.com/google/go-cmp/cmp/options.go b/vendor/github.com/google/go-cmp/cmp/options.go
new file mode 100644
index 00000000..91d4b066
--- /dev/null
+++ b/vendor/github.com/google/go-cmp/cmp/options.go
@@ -0,0 +1,453 @@
+// Copyright 2017, The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE.md file.
+
+package cmp
+
+import (
+	"fmt"
+	"reflect"
+	"runtime"
+	"strings"
+
+	"github.com/google/go-cmp/cmp/internal/function"
+)
+
+// Option configures for specific behavior of Equal and Diff. In particular,
+// the fundamental Option functions (Ignore, Transformer, and Comparer),
+// configure how equality is determined.
+//
+// The fundamental options may be composed with filters (FilterPath and
+// FilterValues) to control the scope over which they are applied.
+//
+// The cmp/cmpopts package provides helper functions for creating options that
+// may be used with Equal and Diff.
+type Option interface {
+	// filter applies all filters and returns the option that remains.
+	// Each option may only read s.curPath and call s.callTTBFunc.
+	//
+	// An Options is returned only if multiple comparers or transformers
+	// can apply simultaneously and will only contain values of those types
+	// or sub-Options containing values of those types.
+	filter(s *state, vx, vy reflect.Value, t reflect.Type) applicableOption
+}
+
+// applicableOption represents the following types:
+//	Fundamental: ignore | invalid | *comparer | *transformer
+//	Grouping:    Options
+type applicableOption interface {
+	Option
+
+	// apply executes the option, which may mutate s or panic.
+	apply(s *state, vx, vy reflect.Value)
+}
+
+// coreOption represents the following types:
+//	Fundamental: ignore | invalid | *comparer | *transformer
+//	Filters:     *pathFilter | *valuesFilter
+type coreOption interface {
+	Option
+	isCore()
+}
+
+type core struct{}
+
+func (core) isCore() {}
+
+// Options is a list of Option values that also satisfies the Option interface.
+// Helper comparison packages may return an Options value when packing multiple
+// Option values into a single Option. When this package processes an Options,
+// it will be implicitly expanded into a flat list.
+//
+// Applying a filter on an Options is equivalent to applying that same filter
+// on all individual options held within.
+type Options []Option
+
+func (opts Options) filter(s *state, vx, vy reflect.Value, t reflect.Type) (out applicableOption) {
+	for _, opt := range opts {
+		switch opt := opt.filter(s, vx, vy, t); opt.(type) {
+		case ignore:
+			return ignore{} // Only ignore can short-circuit evaluation
+		case invalid:
+			out = invalid{} // Takes precedence over comparer or transformer
+		case *comparer, *transformer, Options:
+			switch out.(type) {
+			case nil:
+				out = opt
+			case invalid:
+				// Keep invalid
+			case *comparer, *transformer, Options:
+				out = Options{out, opt} // Conflicting comparers or transformers
+			}
+		}
+	}
+	return out
+}
+
+func (opts Options) apply(s *state, _, _ reflect.Value) {
+	const warning = "ambiguous set of applicable options"
+	const help = "consider using filters to ensure at most one Comparer or Transformer may apply"
+	var ss []string
+	for _, opt := range flattenOptions(nil, opts) {
+		ss = append(ss, fmt.Sprint(opt))
+	}
+	set := strings.Join(ss, "\n\t")
+	panic(fmt.Sprintf("%s at %#v:\n\t%s\n%s", warning, s.curPath, set, help))
+}
+
+func (opts Options) String() string {
+	var ss []string
+	for _, opt := range opts {
+		ss = append(ss, fmt.Sprint(opt))
+	}
+	return fmt.Sprintf("Options{%s}", strings.Join(ss, ", "))
+}
+
+// FilterPath returns a new Option where opt is only evaluated if filter f
+// returns true for the current Path in the value tree.
+//
+// The option passed in may be an Ignore, Transformer, Comparer, Options, or
+// a previously filtered Option.
+func FilterPath(f func(Path) bool, opt Option) Option {
+	if f == nil {
+		panic("invalid path filter function")
+	}
+	if opt := normalizeOption(opt); opt != nil {
+		return &pathFilter{fnc: f, opt: opt}
+	}
+	return nil
+}
+
+type pathFilter struct {
+	core
+	fnc func(Path) bool
+	opt Option
+}
+
+func (f pathFilter) filter(s *state, vx, vy reflect.Value, t reflect.Type) applicableOption {
+	if f.fnc(s.curPath) {
+		return f.opt.filter(s, vx, vy, t)
+	}
+	return nil
+}
+
+func (f pathFilter) String() string {
+	fn := getFuncName(reflect.ValueOf(f.fnc).Pointer())
+	return fmt.Sprintf("FilterPath(%s, %v)", fn, f.opt)
+}
+
+// FilterValues returns a new Option where opt is only evaluated if filter f,
+// which is a function of the form "func(T, T) bool", returns true for the
+// current pair of values being compared. If the type of the values is not
+// assignable to T, then this filter implicitly returns false.
+//
+// The filter function must be
+// symmetric (i.e., agnostic to the order of the inputs) and
+// deterministic (i.e., produces the same result when given the same inputs).
+// If T is an interface, it is possible that f is called with two values with
+// different concrete types that both implement T.
+//
+// The option passed in may be an Ignore, Transformer, Comparer, Options, or
+// a previously filtered Option.
+func FilterValues(f interface{}, opt Option) Option {
+	v := reflect.ValueOf(f)
+	if !function.IsType(v.Type(), function.ValueFilter) || v.IsNil() {
+		panic(fmt.Sprintf("invalid values filter function: %T", f))
+	}
+	if opt := normalizeOption(opt); opt != nil {
+		vf := &valuesFilter{fnc: v, opt: opt}
+		if ti := v.Type().In(0); ti.Kind() != reflect.Interface || ti.NumMethod() > 0 {
+			vf.typ = ti
+		}
+		return vf
+	}
+	return nil
+}
+
+type valuesFilter struct {
+	core
+	typ reflect.Type  // T
+	fnc reflect.Value // func(T, T) bool
+	opt Option
+}
+
+func (f valuesFilter) filter(s *state, vx, vy reflect.Value, t reflect.Type) applicableOption {
+	if !vx.IsValid() || !vy.IsValid() {
+		return invalid{}
+	}
+	if (f.typ == nil || t.AssignableTo(f.typ)) && s.callTTBFunc(f.fnc, vx, vy) {
+		return f.opt.filter(s, vx, vy, t)
+	}
+	return nil
+}
+
+func (f valuesFilter) String() string {
+	fn := getFuncName(f.fnc.Pointer())
+	return fmt.Sprintf("FilterValues(%s, %v)", fn, f.opt)
+}
+
+// Ignore is an Option that causes all comparisons to be ignored.
+// This value is intended to be combined with FilterPath or FilterValues.
+// It is an error to pass an unfiltered Ignore option to Equal.
+func Ignore() Option { return ignore{} }
+
+type ignore struct{ core }
+
+func (ignore) isFiltered() bool                                                     { return false }
+func (ignore) filter(_ *state, _, _ reflect.Value, _ reflect.Type) applicableOption { return ignore{} }
+func (ignore) apply(_ *state, _, _ reflect.Value)                                   { return }
+func (ignore) String() string                                                       { return "Ignore()" }
+
+// invalid is a sentinel Option type to indicate that some options could not
+// be evaluated due to unexported fields.
+type invalid struct{ core }
+
+func (invalid) filter(_ *state, _, _ reflect.Value, _ reflect.Type) applicableOption { return invalid{} }
+func (invalid) apply(s *state, _, _ reflect.Value) {
+	const help = "consider using AllowUnexported or cmpopts.IgnoreUnexported"
+	panic(fmt.Sprintf("cannot handle unexported field: %#v\n%s", s.curPath, help))
+}
+
+// Transformer returns an Option that applies a transformation function that
+// converts values of a certain type into that of another.
+//
+// The transformer f must be a function "func(T) R" that converts values of
+// type T to those of type R and is implicitly filtered to input values
+// assignable to T. The transformer must not mutate T in any way.
+//
+// To help prevent some cases of infinite recursive cycles applying the
+// same transform to the output of itself (e.g., in the case where the
+// input and output types are the same), an implicit filter is added such that
+// a transformer is applicable only if that exact transformer is not already
+// in the tail of the Path since the last non-Transform step.
+//
+// The name is a user provided label that is used as the Transform.Name in the
+// transformation PathStep. If empty, an arbitrary name is used.
+func Transformer(name string, f interface{}) Option {
+	v := reflect.ValueOf(f)
+	if !function.IsType(v.Type(), function.Transformer) || v.IsNil() {
+		panic(fmt.Sprintf("invalid transformer function: %T", f))
+	}
+	if name == "" {
+		name = "λ" // Lambda-symbol as place-holder for anonymous transformer
+	}
+	if !isValid(name) {
+		panic(fmt.Sprintf("invalid name: %q", name))
+	}
+	tr := &transformer{name: name, fnc: reflect.ValueOf(f)}
+	if ti := v.Type().In(0); ti.Kind() != reflect.Interface || ti.NumMethod() > 0 {
+		tr.typ = ti
+	}
+	return tr
+}
+
+type transformer struct {
+	core
+	name string
+	typ  reflect.Type  // T
+	fnc  reflect.Value // func(T) R
+}
+
+func (tr *transformer) isFiltered() bool { return tr.typ != nil }
+
+func (tr *transformer) filter(s *state, _, _ reflect.Value, t reflect.Type) applicableOption {
+	for i := len(s.curPath) - 1; i >= 0; i-- {
+		if t, ok := s.curPath[i].(*transform); !ok {
+			break // Hit most recent non-Transform step
+		} else if tr == t.trans {
+			return nil // Cannot directly use same Transform
+		}
+	}
+	if tr.typ == nil || t.AssignableTo(tr.typ) {
+		return tr
+	}
+	return nil
+}
+
+func (tr *transformer) apply(s *state, vx, vy reflect.Value) {
+	// Update path before calling the Transformer so that dynamic checks
+	// will use the updated path.
+	s.curPath.push(&transform{pathStep{tr.fnc.Type().Out(0)}, tr})
+	defer s.curPath.pop()
+
+	vx = s.callTRFunc(tr.fnc, vx)
+	vy = s.callTRFunc(tr.fnc, vy)
+	s.compareAny(vx, vy)
+}
+
+func (tr transformer) String() string {
+	return fmt.Sprintf("Transformer(%s, %s)", tr.name, getFuncName(tr.fnc.Pointer()))
+}
+
+// Comparer returns an Option that determines whether two values are equal
+// to each other.
+//
+// The comparer f must be a function "func(T, T) bool" and is implicitly
+// filtered to input values assignable to T. If T is an interface, it is
+// possible that f is called with two values of different concrete types that
+// both implement T.
+//
+// The equality function must be:
+//	• Symmetric: equal(x, y) == equal(y, x)
+//	• Deterministic: equal(x, y) == equal(x, y)
+//	• Pure: equal(x, y) does not modify x or y
+func Comparer(f interface{}) Option {
+	v := reflect.ValueOf(f)
+	if !function.IsType(v.Type(), function.Equal) || v.IsNil() {
+		panic(fmt.Sprintf("invalid comparer function: %T", f))
+	}
+	cm := &comparer{fnc: v}
+	if ti := v.Type().In(0); ti.Kind() != reflect.Interface || ti.NumMethod() > 0 {
+		cm.typ = ti
+	}
+	return cm
+}
+
+type comparer struct {
+	core
+	typ reflect.Type  // T
+	fnc reflect.Value // func(T, T) bool
+}
+
+func (cm *comparer) isFiltered() bool { return cm.typ != nil }
+
+func (cm *comparer) filter(_ *state, _, _ reflect.Value, t reflect.Type) applicableOption {
+	if cm.typ == nil || t.AssignableTo(cm.typ) {
+		return cm
+	}
+	return nil
+}
+
+func (cm *comparer) apply(s *state, vx, vy reflect.Value) {
+	eq := s.callTTBFunc(cm.fnc, vx, vy)
+	s.report(eq, vx, vy)
+}
+
+func (cm comparer) String() string {
+	return fmt.Sprintf("Comparer(%s)", getFuncName(cm.fnc.Pointer()))
+}
+
+// AllowUnexported returns an Option that forcibly allows operations on
+// unexported fields in certain structs, which are specified by passing in a
+// value of each struct type.
+//
+// Users of this option must understand that comparing on unexported fields
+// from external packages is not safe since changes in the internal
+// implementation of some external package may cause the result of Equal
+// to unexpectedly change. However, it may be valid to use this option on types
+// defined in an internal package where the semantic meaning of an unexported
+// field is in the control of the user.
+//
+// For some cases, a custom Comparer should be used instead that defines
+// equality as a function of the public API of a type rather than the underlying
+// unexported implementation.
+//
+// For example, the reflect.Type documentation defines equality to be determined
+// by the == operator on the interface (essentially performing a shallow pointer
+// comparison) and most attempts to compare *regexp.Regexp types are interested
+// in only checking that the regular expression strings are equal.
+// Both of these are accomplished using Comparers:
+//
+//	Comparer(func(x, y reflect.Type) bool { return x == y })
+//	Comparer(func(x, y *regexp.Regexp) bool { return x.String() == y.String() })
+//
+// In other cases, the cmpopts.IgnoreUnexported option can be used to ignore
+// all unexported fields on specified struct types.
+func AllowUnexported(types ...interface{}) Option {
+	if !supportAllowUnexported {
+		panic("AllowUnexported is not supported on purego builds, Google App Engine Standard, or GopherJS")
+	}
+	m := make(map[reflect.Type]bool)
+	for _, typ := range types {
+		t := reflect.TypeOf(typ)
+		if t.Kind() != reflect.Struct {
+			panic(fmt.Sprintf("invalid struct type: %T", typ))
+		}
+		m[t] = true
+	}
+	return visibleStructs(m)
+}
+
+type visibleStructs map[reflect.Type]bool
+
+func (visibleStructs) filter(_ *state, _, _ reflect.Value, _ reflect.Type) applicableOption {
+	panic("not implemented")
+}
+
+// reporter is an Option that configures how differences are reported.
+type reporter interface {
+	// TODO: Not exported yet.
+	//
+	// Perhaps add PushStep and PopStep and change Report to only accept
+	// a PathStep instead of the full-path? Adding a PushStep and PopStep makes
+	// it clear that we are traversing the value tree in a depth-first-search
+	// manner, which has an effect on how values are printed.
+
+	Option
+
+	// Report is called for every comparison made and will be provided with
+	// the two values being compared, the equality result, and the
+	// current path in the value tree. It is possible for x or y to be an
+	// invalid reflect.Value if one of the values is non-existent;
+	// which is possible with maps and slices.
+	Report(x, y reflect.Value, eq bool, p Path)
+}
+
+// normalizeOption normalizes the input options such that all Options groups
+// are flattened and groups with a single element are reduced to that element.
+// Only coreOptions and Options containing coreOptions are allowed.
+func normalizeOption(src Option) Option {
+	switch opts := flattenOptions(nil, Options{src}); len(opts) {
+	case 0:
+		return nil
+	case 1:
+		return opts[0]
+	default:
+		return opts
+	}
+}
+
+// flattenOptions copies all options in src to dst as a flat list.
+// Only coreOptions and Options containing coreOptions are allowed.
+func flattenOptions(dst, src Options) Options {
+	for _, opt := range src {
+		switch opt := opt.(type) {
+		case nil:
+			continue
+		case Options:
+			dst = flattenOptions(dst, opt)
+		case coreOption:
+			dst = append(dst, opt)
+		default:
+			panic(fmt.Sprintf("invalid option type: %T", opt))
+		}
+	}
+	return dst
+}
+
+// getFuncName returns a short function name from the pointer.
+// The string parsing logic works up until Go1.9.
+func getFuncName(p uintptr) string {
+	fnc := runtime.FuncForPC(p)
+	if fnc == nil {
+		return "<unknown>"
+	}
+	name := fnc.Name() // E.g., "long/path/name/mypkg.(mytype).(long/path/name/mypkg.myfunc)-fm"
+	if strings.HasSuffix(name, ")-fm") || strings.HasSuffix(name, ")·fm") {
+		// Strip the package name from method name.
+		name = strings.TrimSuffix(name, ")-fm")
+		name = strings.TrimSuffix(name, ")·fm")
+		if i := strings.LastIndexByte(name, '('); i >= 0 {
+			methodName := name[i+1:] // E.g., "long/path/name/mypkg.myfunc"
+			if j := strings.LastIndexByte(methodName, '.'); j >= 0 {
+				methodName = methodName[j+1:] // E.g., "myfunc"
+			}
+			name = name[:i] + methodName // E.g., "long/path/name/mypkg.(mytype)." + "myfunc"
+		}
+	}
+	if i := strings.LastIndexByte(name, '/'); i >= 0 {
+		// Strip the package name.
+		name = name[i+1:] // E.g., "mypkg.(mytype).myfunc"
+	}
+	return name
+}
diff --git a/vendor/github.com/google/go-cmp/cmp/path.go b/vendor/github.com/google/go-cmp/cmp/path.go
new file mode 100644
index 00000000..c08a3cf8
--- /dev/null
+++ b/vendor/github.com/google/go-cmp/cmp/path.go
@@ -0,0 +1,309 @@
+// Copyright 2017, The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE.md file.
+
+package cmp
+
+import (
+	"fmt"
+	"reflect"
+	"strings"
+	"unicode"
+	"unicode/utf8"
+)
+
+type (
+	// Path is a list of PathSteps describing the sequence of operations to get
+	// from some root type to the current position in the value tree.
+	// The first Path element is always an operation-less PathStep that exists
+	// simply to identify the initial type.
+	//
+	// When traversing structs with embedded structs, the embedded struct will
+	// always be accessed as a field before traversing the fields of the
+	// embedded struct themselves. That is, an exported field from the
+	// embedded struct will never be accessed directly from the parent struct.
+	Path []PathStep
+
+	// PathStep is a union-type for specific operations to traverse
+	// a value's tree structure. Users of this package never need to implement
+	// these types as values of this type will be returned by this package.
+	PathStep interface {
+		String() string
+		Type() reflect.Type // Resulting type after performing the path step
+		isPathStep()
+	}
+
+	// SliceIndex is an index operation on a slice or array at some index Key.
+	SliceIndex interface {
+		PathStep
+		Key() int // May return -1 if in a split state
+
+		// SplitKeys returns the indexes for indexing into slices in the
+		// x and y values, respectively. These indexes may differ due to the
+		// insertion or removal of an element in one of the slices, causing
+		// all of the indexes to be shifted. If an index is -1, then that
+		// indicates that the element does not exist in the associated slice.
+		//
+		// Key is guaranteed to return -1 if and only if the indexes returned
+		// by SplitKeys are not the same. SplitKeys will never return -1 for
+		// both indexes.
+		SplitKeys() (x int, y int)
+
+		isSliceIndex()
+	}
+	// MapIndex is an index operation on a map at some index Key.
+	MapIndex interface {
+		PathStep
+		Key() reflect.Value
+		isMapIndex()
+	}
+	// TypeAssertion represents a type assertion on an interface.
+	TypeAssertion interface {
+		PathStep
+		isTypeAssertion()
+	}
+	// StructField represents a struct field access on a field called Name.
+	StructField interface {
+		PathStep
+		Name() string
+		Index() int
+		isStructField()
+	}
+	// Indirect represents pointer indirection on the parent type.
+	Indirect interface {
+		PathStep
+		isIndirect()
+	}
+	// Transform is a transformation from the parent type to the current type.
+	Transform interface {
+		PathStep
+		Name() string
+		Func() reflect.Value
+
+		// Option returns the originally constructed Transformer option.
+		// The == operator can be used to detect the exact option used.
+		Option() Option
+
+		isTransform()
+	}
+)
+
+func (pa *Path) push(s PathStep) {
+	*pa = append(*pa, s)
+}
+
+func (pa *Path) pop() {
+	*pa = (*pa)[:len(*pa)-1]
+}
+
+// Last returns the last PathStep in the Path.
+// If the path is empty, this returns a non-nil PathStep that reports a nil Type.
+func (pa Path) Last() PathStep {
+	return pa.Index(-1)
+}
+
+// Index returns the ith step in the Path and supports negative indexing.
+// A negative index starts counting from the tail of the Path such that -1
+// refers to the last step, -2 refers to the second-to-last step, and so on.
+// If index is invalid, this returns a non-nil PathStep that reports a nil Type.
+func (pa Path) Index(i int) PathStep {
+	if i < 0 {
+		i = len(pa) + i
+	}
+	if i < 0 || i >= len(pa) {
+		return pathStep{}
+	}
+	return pa[i]
+}
+
+// String returns the simplified path to a node.
+// The simplified path only contains struct field accesses.
+//
+// For example:
+//	MyMap.MySlices.MyField
+func (pa Path) String() string {
+	var ss []string
+	for _, s := range pa {
+		if _, ok := s.(*structField); ok {
+			ss = append(ss, s.String())
+		}
+	}
+	return strings.TrimPrefix(strings.Join(ss, ""), ".")
+}
+
+// GoString returns the path to a specific node using Go syntax.
+//
+// For example:
+//	(*root.MyMap["key"].(*mypkg.MyStruct).MySlices)[2][3].MyField
+func (pa Path) GoString() string {
+	var ssPre, ssPost []string
+	var numIndirect int
+	for i, s := range pa {
+		var nextStep PathStep
+		if i+1 < len(pa) {
+			nextStep = pa[i+1]
+		}
+		switch s := s.(type) {
+		case *indirect:
+			numIndirect++
+			pPre, pPost := "(", ")"
+			switch nextStep.(type) {
+			case *indirect:
+				continue // Next step is indirection, so let them batch up
+			case *structField:
+				numIndirect-- // Automatic indirection on struct fields
+			case nil:
+				pPre, pPost = "", "" // Last step; no need for parenthesis
+			}
+			if numIndirect > 0 {
+				ssPre = append(ssPre, pPre+strings.Repeat("*", numIndirect))
+				ssPost = append(ssPost, pPost)
+			}
+			numIndirect = 0
+			continue
+		case *transform:
+			ssPre = append(ssPre, s.trans.name+"(")
+			ssPost = append(ssPost, ")")
+			continue
+		case *typeAssertion:
+			// As a special-case, elide type assertions on anonymous types
+			// since they are typically generated dynamically and can be very
+			// verbose. For example, some transforms return interface{} because
+			// of Go's lack of generics, but typically take in and return the
+			// exact same concrete type.
+			if s.Type().PkgPath() == "" {
+				continue
+			}
+		}
+		ssPost = append(ssPost, s.String())
+	}
+	for i, j := 0, len(ssPre)-1; i < j; i, j = i+1, j-1 {
+		ssPre[i], ssPre[j] = ssPre[j], ssPre[i]
+	}
+	return strings.Join(ssPre, "") + strings.Join(ssPost, "")
+}
+
+type (
+	pathStep struct {
+		typ reflect.Type
+	}
+
+	sliceIndex struct {
+		pathStep
+		xkey, ykey int
+	}
+	mapIndex struct {
+		pathStep
+		key reflect.Value
+	}
+	typeAssertion struct {
+		pathStep
+	}
+	structField struct {
+		pathStep
+		name string
+		idx  int
+
+		// These fields are used for forcibly accessing an unexported field.
+		// pvx, pvy, and field are only valid if unexported is true.
+		unexported bool
+		force      bool                // Forcibly allow visibility
+		pvx, pvy   reflect.Value       // Parent values
+		field      reflect.StructField // Field information
+	}
+	indirect struct {
+		pathStep
+	}
+	transform struct {
+		pathStep
+		trans *transformer
+	}
+)
+
+func (ps pathStep) Type() reflect.Type { return ps.typ }
+func (ps pathStep) String() string {
+	if ps.typ == nil {
+		return "<nil>"
+	}
+	s := ps.typ.String()
+	if s == "" || strings.ContainsAny(s, "{}\n") {
+		return "root" // Type too simple or complex to print
+	}
+	return fmt.Sprintf("{%s}", s)
+}
+
+func (si sliceIndex) String() string {
+	switch {
+	case si.xkey == si.ykey:
+		return fmt.Sprintf("[%d]", si.xkey)
+	case si.ykey == -1:
+		// [5->?] means "I don't know where X[5] went"
+		return fmt.Sprintf("[%d->?]", si.xkey)
+	case si.xkey == -1:
+		// [?->3] means "I don't know where Y[3] came from"
+		return fmt.Sprintf("[?->%d]", si.ykey)
+	default:
+		// [5->3] means "X[5] moved to Y[3]"
+		return fmt.Sprintf("[%d->%d]", si.xkey, si.ykey)
+	}
+}
+func (mi mapIndex) String() string      { return fmt.Sprintf("[%#v]", mi.key) }
+func (ta typeAssertion) String() string { return fmt.Sprintf(".(%v)", ta.typ) }
+func (sf structField) String() string   { return fmt.Sprintf(".%s", sf.name) }
+func (in indirect) String() string      { return "*" }
+func (tf transform) String() string     { return fmt.Sprintf("%s()", tf.trans.name) }
+
+func (si sliceIndex) Key() int {
+	if si.xkey != si.ykey {
+		return -1
+	}
+	return si.xkey
+}
+func (si sliceIndex) SplitKeys() (x, y int) { return si.xkey, si.ykey }
+func (mi mapIndex) Key() reflect.Value      { return mi.key }
+func (sf structField) Name() string         { return sf.name }
+func (sf structField) Index() int           { return sf.idx }
+func (tf transform) Name() string           { return tf.trans.name }
+func (tf transform) Func() reflect.Value    { return tf.trans.fnc }
+func (tf transform) Option() Option         { return tf.trans }
+
+func (pathStep) isPathStep()           {}
+func (sliceIndex) isSliceIndex()       {}
+func (mapIndex) isMapIndex()           {}
+func (typeAssertion) isTypeAssertion() {}
+func (structField) isStructField()     {}
+func (indirect) isIndirect()           {}
+func (transform) isTransform()         {}
+
+var (
+	_ SliceIndex    = sliceIndex{}
+	_ MapIndex      = mapIndex{}
+	_ TypeAssertion = typeAssertion{}
+	_ StructField   = structField{}
+	_ Indirect      = indirect{}
+	_ Transform     = transform{}
+
+	_ PathStep = sliceIndex{}
+	_ PathStep = mapIndex{}
+	_ PathStep = typeAssertion{}
+	_ PathStep = structField{}
+	_ PathStep = indirect{}
+	_ PathStep = transform{}
+)
+
+// isExported reports whether the identifier is exported.
+func isExported(id string) bool {
+	r, _ := utf8.DecodeRuneInString(id)
+	return unicode.IsUpper(r)
+}
+
+// isValid reports whether the identifier is valid.
+// Empty and underscore-only strings are not valid.
+func isValid(id string) bool {
+	ok := id != "" && id != "_"
+	for j, c := range id {
+		ok = ok && (j > 0 || !unicode.IsDigit(c))
+		ok = ok && (c == '_' || unicode.IsLetter(c) || unicode.IsDigit(c))
+	}
+	return ok
+}
diff --git a/vendor/github.com/google/go-cmp/cmp/reporter.go b/vendor/github.com/google/go-cmp/cmp/reporter.go
new file mode 100644
index 00000000..20e9f18e
--- /dev/null
+++ b/vendor/github.com/google/go-cmp/cmp/reporter.go
@@ -0,0 +1,53 @@
+// Copyright 2017, The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE.md file.
+
+package cmp
+
+import (
+	"fmt"
+	"reflect"
+	"strings"
+
+	"github.com/google/go-cmp/cmp/internal/value"
+)
+
+type defaultReporter struct {
+	Option
+	diffs  []string // List of differences, possibly truncated
+	ndiffs int      // Total number of differences
+	nbytes int      // Number of bytes in diffs
+	nlines int      // Number of lines in diffs
+}
+
+var _ reporter = (*defaultReporter)(nil)
+
+func (r *defaultReporter) Report(x, y reflect.Value, eq bool, p Path) {
+	if eq {
+		return // Ignore equal results
+	}
+	const maxBytes = 4096
+	const maxLines = 256
+	r.ndiffs++
+	if r.nbytes < maxBytes && r.nlines < maxLines {
+		sx := value.Format(x, value.FormatConfig{UseStringer: true})
+		sy := value.Format(y, value.FormatConfig{UseStringer: true})
+		if sx == sy {
+			// Unhelpful output, so use more exact formatting.
+			sx = value.Format(x, value.FormatConfig{PrintPrimitiveType: true})
+			sy = value.Format(y, value.FormatConfig{PrintPrimitiveType: true})
+		}
+		s := fmt.Sprintf("%#v:\n\t-: %s\n\t+: %s\n", p, sx, sy)
+		r.diffs = append(r.diffs, s)
+		r.nbytes += len(s)
+		r.nlines += strings.Count(s, "\n")
+	}
+}
+
+func (r *defaultReporter) String() string {
+	s := strings.Join(r.diffs, "")
+	if r.ndiffs == len(r.diffs) {
+		return s
+	}
+	return fmt.Sprintf("%s... %d more differences ...", s, r.ndiffs-len(r.diffs))
+}
diff --git a/vendor/github.com/google/go-cmp/cmp/unsafe_panic.go b/vendor/github.com/google/go-cmp/cmp/unsafe_panic.go
new file mode 100644
index 00000000..d1518eb3
--- /dev/null
+++ b/vendor/github.com/google/go-cmp/cmp/unsafe_panic.go
@@ -0,0 +1,15 @@
+// Copyright 2017, The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE.md file.
+
+// +build purego appengine js
+
+package cmp
+
+import "reflect"
+
+const supportAllowUnexported = false
+
+func unsafeRetrieveField(reflect.Value, reflect.StructField) reflect.Value {
+	panic("unsafeRetrieveField is not implemented")
+}
diff --git a/vendor/github.com/google/go-cmp/cmp/unsafe_reflect.go b/vendor/github.com/google/go-cmp/cmp/unsafe_reflect.go
new file mode 100644
index 00000000..579b6550
--- /dev/null
+++ b/vendor/github.com/google/go-cmp/cmp/unsafe_reflect.go
@@ -0,0 +1,23 @@
+// Copyright 2017, The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE.md file.
+
+// +build !purego,!appengine,!js
+
+package cmp
+
+import (
+	"reflect"
+	"unsafe"
+)
+
+const supportAllowUnexported = true
+
+// unsafeRetrieveField uses unsafe to forcibly retrieve any field from a struct
+// such that the value has read-write permissions.
+//
+// The parent struct, v, must be addressable, while f must be a StructField
+// describing the field to retrieve.
+func unsafeRetrieveField(v reflect.Value, f reflect.StructField) reflect.Value {
+	return reflect.NewAt(f.Type, unsafe.Pointer(v.UnsafeAddr()+f.Offset)).Elem()
+}
diff --git a/vendor/gotest.tools/LICENSE b/vendor/gotest.tools/LICENSE
new file mode 100644
index 00000000..d6456956
--- /dev/null
+++ b/vendor/gotest.tools/LICENSE
@@ -0,0 +1,202 @@
+
+                                 Apache License
+                           Version 2.0, January 2004
+                        http://www.apache.org/licenses/
+
+   TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
+   1. Definitions.
+
+      "License" shall mean the terms and conditions for use, reproduction,
+      and distribution as defined by Sections 1 through 9 of this document.
+
+      "Licensor" shall mean the copyright owner or entity authorized by
+      the copyright owner that is granting the License.
+
+      "Legal Entity" shall mean the union of the acting entity and all
+      other entities that control, are controlled by, or are under common
+      control with that entity. For the purposes of this definition,
+      "control" means (i) the power, direct or indirect, to cause the
+      direction or management of such entity, whether by contract or
+      otherwise, or (ii) ownership of fifty percent (50%) or more of the
+      outstanding shares, or (iii) beneficial ownership of such entity.
+
+      "You" (or "Your") shall mean an individual or Legal Entity
+      exercising permissions granted by this License.
+
+      "Source" form shall mean the preferred form for making modifications,
+      including but not limited to software source code, documentation
+      source, and configuration files.
+
+      "Object" form shall mean any form resulting from mechanical
+      transformation or translation of a Source form, including but
+      not limited to compiled object code, generated documentation,
+      and conversions to other media types.
+
+      "Work" shall mean the work of authorship, whether in Source or
+      Object form, made available under the License, as indicated by a
+      copyright notice that is included in or attached to the work
+      (an example is provided in the Appendix below).
+
+      "Derivative Works" shall mean any work, whether in Source or Object
+      form, that is based on (or derived from) the Work and for which the
+      editorial revisions, annotations, elaborations, or other modifications
+      represent, as a whole, an original work of authorship. For the purposes
+      of this License, Derivative Works shall not include works that remain
+      separable from, or merely link (or bind by name) to the interfaces of,
+      the Work and Derivative Works thereof.
+
+      "Contribution" shall mean any work of authorship, including
+      the original version of the Work and any modifications or additions
+      to that Work or Derivative Works thereof, that is intentionally
+      submitted to Licensor for inclusion in the Work by the copyright owner
+      or by an individual or Legal Entity authorized to submit on behalf of
+      the copyright owner. For the purposes of this definition, "submitted"
+      means any form of electronic, verbal, or written communication sent
+      to the Licensor or its representatives, including but not limited to
+      communication on electronic mailing lists, source code control systems,
+      and issue tracking systems that are managed by, or on behalf of, the
+      Licensor for the purpose of discussing and improving the Work, but
+      excluding communication that is conspicuously marked or otherwise
+      designated in writing by the copyright owner as "Not a Contribution."
+
+      "Contributor" shall mean Licensor and any individual or Legal Entity
+      on behalf of whom a Contribution has been received by Licensor and
+      subsequently incorporated within the Work.
+
+   2. Grant of Copyright License. Subject to the terms and conditions of
+      this License, each Contributor hereby grants to You a perpetual,
+      worldwide, non-exclusive, no-charge, royalty-free, irrevocable
+      copyright license to reproduce, prepare Derivative Works of,
+      publicly display, publicly perform, sublicense, and distribute the
+      Work and such Derivative Works in Source or Object form.
+
+   3. Grant of Patent License. Subject to the terms and conditions of
+      this License, each Contributor hereby grants to You a perpetual,
+      worldwide, non-exclusive, no-charge, royalty-free, irrevocable
+      (except as stated in this section) patent license to make, have made,
+      use, offer to sell, sell, import, and otherwise transfer the Work,
+      where such license applies only to those patent claims licensable
+      by such Contributor that are necessarily infringed by their
+      Contribution(s) alone or by combination of their Contribution(s)
+      with the Work to which such Contribution(s) was submitted. If You
+      institute patent litigation against any entity (including a
+      cross-claim or counterclaim in a lawsuit) alleging that the Work
+      or a Contribution incorporated within the Work constitutes direct
+      or contributory patent infringement, then any patent licenses
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+
+   4. Redistribution. You may reproduce and distribute copies of the
+      Work or Derivative Works thereof in any medium, with or without
+      modifications, and in Source or Object form, provided that You
+      meet the following conditions:
+
+      (a) You must give any other recipients of the Work or
+          Derivative Works a copy of this License; and
+
+      (b) You must cause any modified files to carry prominent notices
+          stating that You changed the files; and
+
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+
+      (d) If the Work includes a "NOTICE" text file as part of its
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+          of the NOTICE file are for informational purposes only and
+          do not modify the License. You may add Your own attribution
+          notices within Derivative Works that You distribute, alongside
+          or as an addendum to the NOTICE text from the Work, provided
+          that such additional attribution notices cannot be construed
+          as modifying the License.
+
+      You may add Your own copyright statement to Your modifications and
+      may provide additional or different license terms and conditions
+      for use, reproduction, or distribution of Your modifications, or
+      for any such Derivative Works as a whole, provided Your use,
+      reproduction, and distribution of the Work otherwise complies with
+      the conditions stated in this License.
+
+   5. Submission of Contributions. Unless You explicitly state otherwise,
+      any Contribution intentionally submitted for inclusion in the Work
+      by You to the Licensor shall be under the terms and conditions of
+      this License, without any additional terms or conditions.
+      Notwithstanding the above, nothing herein shall supersede or modify
+      the terms of any separate license agreement you may have executed
+      with Licensor regarding such Contributions.
+
+   6. Trademarks. This License does not grant permission to use the trade
+      names, trademarks, service marks, or product names of the Licensor,
+      except as required for reasonable and customary use in describing the
+      origin of the Work and reproducing the content of the NOTICE file.
+
+   7. Disclaimer of Warranty. Unless required by applicable law or
+      agreed to in writing, Licensor provides the Work (and each
+      Contributor provides its Contributions) on an "AS IS" BASIS,
+      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
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+      PARTICULAR PURPOSE. You are solely responsible for determining the
+      appropriateness of using or redistributing the Work and assume any
+      risks associated with Your exercise of permissions under this License.
+
+   8. Limitation of Liability. In no event and under no legal theory,
+      whether in tort (including negligence), contract, or otherwise,
+      unless required by applicable law (such as deliberate and grossly
+      negligent acts) or agreed to in writing, shall any Contributor be
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+      of any other Contributor, and only if You agree to indemnify,
+      defend, and hold each Contributor harmless for any liability
+      incurred by, or claims asserted against, such Contributor by reason
+      of your accepting any such warranty or additional liability.
+
+   END OF TERMS AND CONDITIONS
+
+   APPENDIX: How to apply the Apache License to your work.
+
+      To apply the Apache License to your work, attach the following
+      boilerplate notice, with the fields enclosed by brackets "[]"
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+      file or class name and description of purpose be included on the
+      same "printed page" as the copyright notice for easier
+      identification within third-party archives.
+
+   Copyright [yyyy] [name of copyright owner]
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
diff --git a/vendor/gotest.tools/assert/assert.go b/vendor/gotest.tools/assert/assert.go
new file mode 100644
index 00000000..05d66354
--- /dev/null
+++ b/vendor/gotest.tools/assert/assert.go
@@ -0,0 +1,311 @@
+/*Package assert provides assertions for comparing expected values to actual
+values. When an assertion fails a helpful error message is printed.
+
+Assert and Check
+
+Assert() and Check() both accept a Comparison, and fail the test when the
+comparison fails. The one difference is that Assert() will end the test execution
+immediately (using t.FailNow()) whereas Check() will fail the test (using t.Fail()),
+return the value of the comparison, then proceed with the rest of the test case.
+
+Example usage
+
+The example below shows assert used with some common types.
+
+
+	import (
+	    "testing"
+
+	    "gotest.tools/assert"
+	    is "gotest.tools/assert/cmp"
+	)
+
+	func TestEverything(t *testing.T) {
+	    // booleans
+	    assert.Assert(t, ok)
+	    assert.Assert(t, !missing)
+
+	    // primitives
+	    assert.Equal(t, count, 1)
+	    assert.Equal(t, msg, "the message")
+	    assert.Assert(t, total != 10) // NotEqual
+
+	    // errors
+	    assert.NilError(t, closer.Close())
+	    assert.Error(t, err, "the exact error message")
+	    assert.ErrorContains(t, err, "includes this")
+	    assert.ErrorType(t, err, os.IsNotExist)
+
+	    // complex types
+	    assert.DeepEqual(t, result, myStruct{Name: "title"})
+	    assert.Assert(t, is.Len(items, 3))
+	    assert.Assert(t, len(sequence) != 0) // NotEmpty
+	    assert.Assert(t, is.Contains(mapping, "key"))
+
+	    // pointers and interface
+	    assert.Assert(t, is.Nil(ref))
+	    assert.Assert(t, ref != nil) // NotNil
+	}
+
+Comparisons
+
+Package https://godoc.org/gotest.tools/assert/cmp provides
+many common comparisons. Additional comparisons can be written to compare
+values in other ways. See the example Assert (CustomComparison).
+
+Automated migration from testify
+
+gty-migrate-from-testify is a binary which can update source code which uses
+testify assertions to use the assertions provided by this package.
+
+See http://bit.do/cmd-gty-migrate-from-testify.
+
+
+*/
+package assert // import "gotest.tools/assert"
+
+import (
+	"fmt"
+	"go/ast"
+	"go/token"
+
+	gocmp "github.com/google/go-cmp/cmp"
+	"gotest.tools/assert/cmp"
+	"gotest.tools/internal/format"
+	"gotest.tools/internal/source"
+)
+
+// BoolOrComparison can be a bool, or cmp.Comparison. See Assert() for usage.
+type BoolOrComparison interface{}
+
+// TestingT is the subset of testing.T used by the assert package.
+type TestingT interface {
+	FailNow()
+	Fail()
+	Log(args ...interface{})
+}
+
+type helperT interface {
+	Helper()
+}
+
+const failureMessage = "assertion failed: "
+
+// nolint: gocyclo
+func assert(
+	t TestingT,
+	failer func(),
+	argSelector argSelector,
+	comparison BoolOrComparison,
+	msgAndArgs ...interface{},
+) bool {
+	if ht, ok := t.(helperT); ok {
+		ht.Helper()
+	}
+	var success bool
+	switch check := comparison.(type) {
+	case bool:
+		if check {
+			return true
+		}
+		logFailureFromBool(t, msgAndArgs...)
+
+	// Undocumented legacy comparison without Result type
+	case func() (success bool, message string):
+		success = runCompareFunc(t, check, msgAndArgs...)
+
+	case nil:
+		return true
+
+	case error:
+		msg := "error is not nil: "
+		t.Log(format.WithCustomMessage(failureMessage+msg+check.Error(), msgAndArgs...))
+
+	case cmp.Comparison:
+		success = runComparison(t, argSelector, check, msgAndArgs...)
+
+	case func() cmp.Result:
+		success = runComparison(t, argSelector, check, msgAndArgs...)
+
+	default:
+		t.Log(fmt.Sprintf("invalid Comparison: %v (%T)", check, check))
+	}
+
+	if success {
+		return true
+	}
+	failer()
+	return false
+}
+
+func runCompareFunc(
+	t TestingT,
+	f func() (success bool, message string),
+	msgAndArgs ...interface{},
+) bool {
+	if ht, ok := t.(helperT); ok {
+		ht.Helper()
+	}
+	if success, message := f(); !success {
+		t.Log(format.WithCustomMessage(failureMessage+message, msgAndArgs...))
+		return false
+	}
+	return true
+}
+
+func logFailureFromBool(t TestingT, msgAndArgs ...interface{}) {
+	if ht, ok := t.(helperT); ok {
+		ht.Helper()
+	}
+	const stackIndex = 3 // Assert()/Check(), assert(), formatFailureFromBool()
+	const comparisonArgPos = 1
+	args, err := source.CallExprArgs(stackIndex)
+	if err != nil {
+		t.Log(err.Error())
+		return
+	}
+
+	msg, err := boolFailureMessage(args[comparisonArgPos])
+	if err != nil {
+		t.Log(err.Error())
+		msg = "expression is false"
+	}
+
+	t.Log(format.WithCustomMessage(failureMessage+msg, msgAndArgs...))
+}
+
+func boolFailureMessage(expr ast.Expr) (string, error) {
+	if binaryExpr, ok := expr.(*ast.BinaryExpr); ok && binaryExpr.Op == token.NEQ {
+		x, err := source.FormatNode(binaryExpr.X)
+		if err != nil {
+			return "", err
+		}
+		y, err := source.FormatNode(binaryExpr.Y)
+		if err != nil {
+			return "", err
+		}
+		return x + " is " + y, nil
+	}
+
+	if unaryExpr, ok := expr.(*ast.UnaryExpr); ok && unaryExpr.Op == token.NOT {
+		x, err := source.FormatNode(unaryExpr.X)
+		if err != nil {
+			return "", err
+		}
+		return x + " is true", nil
+	}
+
+	formatted, err := source.FormatNode(expr)
+	if err != nil {
+		return "", err
+	}
+	return "expression is false: " + formatted, nil
+}
+
+// Assert performs a comparison. If the comparison fails the test is marked as
+// failed, a failure message is logged, and execution is stopped immediately.
+//
+// The comparison argument may be one of three types: bool, cmp.Comparison or
+// error.
+// When called with a bool the failure message will contain the literal source
+// code of the expression.
+// When called with a cmp.Comparison the comparison is responsible for producing
+// a helpful failure message.
+// When called with an error a nil value is considered success. A non-nil error
+// is a failure, and Error() is used as the failure message.
+func Assert(t TestingT, comparison BoolOrComparison, msgAndArgs ...interface{}) {
+	if ht, ok := t.(helperT); ok {
+		ht.Helper()
+	}
+	assert(t, t.FailNow, argsFromComparisonCall, comparison, msgAndArgs...)
+}
+
+// Check performs a comparison. If the comparison fails the test is marked as
+// failed, a failure message is logged, and Check returns false. Otherwise returns
+// true.
+//
+// See Assert for details about the comparison arg and failure messages.
+func Check(t TestingT, comparison BoolOrComparison, msgAndArgs ...interface{}) bool {
+	if ht, ok := t.(helperT); ok {
+		ht.Helper()
+	}
+	return assert(t, t.Fail, argsFromComparisonCall, comparison, msgAndArgs...)
+}
+
+// NilError fails the test immediately if err is not nil.
+// This is equivalent to Assert(t, err)
+func NilError(t TestingT, err error, msgAndArgs ...interface{}) {
+	if ht, ok := t.(helperT); ok {
+		ht.Helper()
+	}
+	assert(t, t.FailNow, argsAfterT, err, msgAndArgs...)
+}
+
+// Equal uses the == operator to assert two values are equal and fails the test
+// if they are not equal.
+//
+// If the comparison fails Equal will use the variable names for x and y as part
+// of the failure message to identify the actual and expected values.
+//
+// If either x or y are a multi-line string the failure message will include a
+// unified diff of the two values. If the values only differ by whitespace
+// the unified diff will be augmented by replacing whitespace characters with
+// visible characters to identify the whitespace difference.
+//
+// This is equivalent to Assert(t, cmp.Equal(x, y)).
+func Equal(t TestingT, x, y interface{}, msgAndArgs ...interface{}) {
+	if ht, ok := t.(helperT); ok {
+		ht.Helper()
+	}
+	assert(t, t.FailNow, argsAfterT, cmp.Equal(x, y), msgAndArgs...)
+}
+
+// DeepEqual uses google/go-cmp (http://bit.do/go-cmp) to assert two values are
+// equal and fails the test if they are not equal.
+//
+// Package https://godoc.org/gotest.tools/assert/opt provides some additional
+// commonly used Options.
+//
+// This is equivalent to Assert(t, cmp.DeepEqual(x, y)).
+func DeepEqual(t TestingT, x, y interface{}, opts ...gocmp.Option) {
+	if ht, ok := t.(helperT); ok {
+		ht.Helper()
+	}
+	assert(t, t.FailNow, argsAfterT, cmp.DeepEqual(x, y, opts...))
+}
+
+// Error fails the test if err is nil, or the error message is not the expected
+// message.
+// Equivalent to Assert(t, cmp.Error(err, message)).
+func Error(t TestingT, err error, message string, msgAndArgs ...interface{}) {
+	if ht, ok := t.(helperT); ok {
+		ht.Helper()
+	}
+	assert(t, t.FailNow, argsAfterT, cmp.Error(err, message), msgAndArgs...)
+}
+
+// ErrorContains fails the test if err is nil, or the error message does not
+// contain the expected substring.
+// Equivalent to Assert(t, cmp.ErrorContains(err, substring)).
+func ErrorContains(t TestingT, err error, substring string, msgAndArgs ...interface{}) {
+	if ht, ok := t.(helperT); ok {
+		ht.Helper()
+	}
+	assert(t, t.FailNow, argsAfterT, cmp.ErrorContains(err, substring), msgAndArgs...)
+}
+
+// ErrorType fails the test if err is nil, or err is not the expected type.
+//
+// Expected can be one of:
+// a func(error) bool which returns true if the error is the expected type,
+// an instance of (or a pointer to) a struct of the expected type,
+// a pointer to an interface the error is expected to implement,
+// a reflect.Type of the expected struct or interface.
+//
+// Equivalent to Assert(t, cmp.ErrorType(err, expected)).
+func ErrorType(t TestingT, err error, expected interface{}, msgAndArgs ...interface{}) {
+	if ht, ok := t.(helperT); ok {
+		ht.Helper()
+	}
+	assert(t, t.FailNow, argsAfterT, cmp.ErrorType(err, expected), msgAndArgs...)
+}
diff --git a/vendor/gotest.tools/assert/cmp/compare.go b/vendor/gotest.tools/assert/cmp/compare.go
new file mode 100644
index 00000000..ae03749e
--- /dev/null
+++ b/vendor/gotest.tools/assert/cmp/compare.go
@@ -0,0 +1,312 @@
+/*Package cmp provides Comparisons for Assert and Check*/
+package cmp // import "gotest.tools/assert/cmp"
+
+import (
+	"fmt"
+	"reflect"
+	"strings"
+
+	"github.com/google/go-cmp/cmp"
+	"gotest.tools/internal/format"
+)
+
+// Comparison is a function which compares values and returns ResultSuccess if
+// the actual value matches the expected value. If the values do not match the
+// Result will contain a message about why it failed.
+type Comparison func() Result
+
+// DeepEqual compares two values using google/go-cmp (http://bit.do/go-cmp)
+// and succeeds if the values are equal.
+//
+// The comparison can be customized using comparison Options.
+// Package https://godoc.org/gotest.tools/assert/opt provides some additional
+// commonly used Options.
+func DeepEqual(x, y interface{}, opts ...cmp.Option) Comparison {
+	return func() (result Result) {
+		defer func() {
+			if panicmsg, handled := handleCmpPanic(recover()); handled {
+				result = ResultFailure(panicmsg)
+			}
+		}()
+		diff := cmp.Diff(x, y, opts...)
+		if diff == "" {
+			return ResultSuccess
+		}
+		return multiLineDiffResult(diff)
+	}
+}
+
+func handleCmpPanic(r interface{}) (string, bool) {
+	if r == nil {
+		return "", false
+	}
+	panicmsg, ok := r.(string)
+	if !ok {
+		panic(r)
+	}
+	switch {
+	case strings.HasPrefix(panicmsg, "cannot handle unexported field"):
+		return panicmsg, true
+	}
+	panic(r)
+}
+
+func toResult(success bool, msg string) Result {
+	if success {
+		return ResultSuccess
+	}
+	return ResultFailure(msg)
+}
+
+// Equal succeeds if x == y. See assert.Equal for full documentation.
+func Equal(x, y interface{}) Comparison {
+	return func() Result {
+		switch {
+		case x == y:
+			return ResultSuccess
+		case isMultiLineStringCompare(x, y):
+			diff := format.UnifiedDiff(format.DiffConfig{A: x.(string), B: y.(string)})
+			return multiLineDiffResult(diff)
+		}
+		return ResultFailureTemplate(`
+			{{- .Data.x}} (
+				{{- with callArg 0 }}{{ formatNode . }} {{end -}}
+				{{- printf "%T" .Data.x -}}
+			) != {{ .Data.y}} (
+				{{- with callArg 1 }}{{ formatNode . }} {{end -}}
+				{{- printf "%T" .Data.y -}}
+			)`,
+			map[string]interface{}{"x": x, "y": y})
+	}
+}
+
+func isMultiLineStringCompare(x, y interface{}) bool {
+	strX, ok := x.(string)
+	if !ok {
+		return false
+	}
+	strY, ok := y.(string)
+	if !ok {
+		return false
+	}
+	return strings.Contains(strX, "\n") || strings.Contains(strY, "\n")
+}
+
+func multiLineDiffResult(diff string) Result {
+	return ResultFailureTemplate(`
+--- {{ with callArg 0 }}{{ formatNode . }}{{else}}←{{end}}
++++ {{ with callArg 1 }}{{ formatNode . }}{{else}}→{{end}}
+{{ .Data.diff }}`,
+		map[string]interface{}{"diff": diff})
+}
+
+// Len succeeds if the sequence has the expected length.
+func Len(seq interface{}, expected int) Comparison {
+	return func() (result Result) {
+		defer func() {
+			if e := recover(); e != nil {
+				result = ResultFailure(fmt.Sprintf("type %T does not have a length", seq))
+			}
+		}()
+		value := reflect.ValueOf(seq)
+		length := value.Len()
+		if length == expected {
+			return ResultSuccess
+		}
+		msg := fmt.Sprintf("expected %s (length %d) to have length %d", seq, length, expected)
+		return ResultFailure(msg)
+	}
+}
+
+// Contains succeeds if item is in collection. Collection may be a string, map,
+// slice, or array.
+//
+// If collection is a string, item must also be a string, and is compared using
+// strings.Contains().
+// If collection is a Map, contains will succeed if item is a key in the map.
+// If collection is a slice or array, item is compared to each item in the
+// sequence using reflect.DeepEqual().
+func Contains(collection interface{}, item interface{}) Comparison {
+	return func() Result {
+		colValue := reflect.ValueOf(collection)
+		if !colValue.IsValid() {
+			return ResultFailure(fmt.Sprintf("nil does not contain items"))
+		}
+		msg := fmt.Sprintf("%v does not contain %v", collection, item)
+
+		itemValue := reflect.ValueOf(item)
+		switch colValue.Type().Kind() {
+		case reflect.String:
+			if itemValue.Type().Kind() != reflect.String {
+				return ResultFailure("string may only contain strings")
+			}
+			return toResult(
+				strings.Contains(colValue.String(), itemValue.String()),
+				fmt.Sprintf("string %q does not contain %q", collection, item))
+
+		case reflect.Map:
+			if itemValue.Type() != colValue.Type().Key() {
+				return ResultFailure(fmt.Sprintf(
+					"%v can not contain a %v key", colValue.Type(), itemValue.Type()))
+			}
+			return toResult(colValue.MapIndex(itemValue).IsValid(), msg)
+
+		case reflect.Slice, reflect.Array:
+			for i := 0; i < colValue.Len(); i++ {
+				if reflect.DeepEqual(colValue.Index(i).Interface(), item) {
+					return ResultSuccess
+				}
+			}
+			return ResultFailure(msg)
+		default:
+			return ResultFailure(fmt.Sprintf("type %T does not contain items", collection))
+		}
+	}
+}
+
+// Panics succeeds if f() panics.
+func Panics(f func()) Comparison {
+	return func() (result Result) {
+		defer func() {
+			if err := recover(); err != nil {
+				result = ResultSuccess
+			}
+		}()
+		f()
+		return ResultFailure("did not panic")
+	}
+}
+
+// Error succeeds if err is a non-nil error, and the error message equals the
+// expected message.
+func Error(err error, message string) Comparison {
+	return func() Result {
+		switch {
+		case err == nil:
+			return ResultFailure("expected an error, got nil")
+		case err.Error() != message:
+			return ResultFailure(fmt.Sprintf(
+				"expected error %q, got %+v", message, err))
+		}
+		return ResultSuccess
+	}
+}
+
+// ErrorContains succeeds if err is a non-nil error, and the error message contains
+// the expected substring.
+func ErrorContains(err error, substring string) Comparison {
+	return func() Result {
+		switch {
+		case err == nil:
+			return ResultFailure("expected an error, got nil")
+		case !strings.Contains(err.Error(), substring):
+			return ResultFailure(fmt.Sprintf(
+				"expected error to contain %q, got %+v", substring, err))
+		}
+		return ResultSuccess
+	}
+}
+
+// Nil succeeds if obj is a nil interface, pointer, or function.
+//
+// Use NilError() for comparing errors. Use Len(obj, 0) for comparing slices,
+// maps, and channels.
+func Nil(obj interface{}) Comparison {
+	msgFunc := func(value reflect.Value) string {
+		return fmt.Sprintf("%v (type %s) is not nil", reflect.Indirect(value), value.Type())
+	}
+	return isNil(obj, msgFunc)
+}
+
+func isNil(obj interface{}, msgFunc func(reflect.Value) string) Comparison {
+	return func() Result {
+		if obj == nil {
+			return ResultSuccess
+		}
+		value := reflect.ValueOf(obj)
+		kind := value.Type().Kind()
+		if kind >= reflect.Chan && kind <= reflect.Slice {
+			if value.IsNil() {
+				return ResultSuccess
+			}
+			return ResultFailure(msgFunc(value))
+		}
+
+		return ResultFailure(fmt.Sprintf("%v (type %s) can not be nil", value, value.Type()))
+	}
+}
+
+// ErrorType succeeds if err is not nil and is of the expected type.
+//
+// Expected can be one of:
+// a func(error) bool which returns true if the error is the expected type,
+// an instance of (or a pointer to) a struct of the expected type,
+// a pointer to an interface the error is expected to implement,
+// a reflect.Type of the expected struct or interface.
+func ErrorType(err error, expected interface{}) Comparison {
+	return func() Result {
+		switch expectedType := expected.(type) {
+		case func(error) bool:
+			return cmpErrorTypeFunc(err, expectedType)
+		case reflect.Type:
+			if expectedType.Kind() == reflect.Interface {
+				return cmpErrorTypeImplementsType(err, expectedType)
+			}
+			return cmpErrorTypeEqualType(err, expectedType)
+		case nil:
+			return ResultFailure(fmt.Sprintf("invalid type for expected: nil"))
+		}
+
+		expectedType := reflect.TypeOf(expected)
+		switch {
+		case expectedType.Kind() == reflect.Struct, isPtrToStruct(expectedType):
+			return cmpErrorTypeEqualType(err, expectedType)
+		case isPtrToInterface(expectedType):
+			return cmpErrorTypeImplementsType(err, expectedType.Elem())
+		}
+		return ResultFailure(fmt.Sprintf("invalid type for expected: %T", expected))
+	}
+}
+
+func cmpErrorTypeFunc(err error, f func(error) bool) Result {
+	if f(err) {
+		return ResultSuccess
+	}
+	actual := "nil"
+	if err != nil {
+		actual = fmt.Sprintf("%s (%T)", err, err)
+	}
+	return ResultFailureTemplate(`error is {{ .Data.actual }}
+		{{- with callArg 1 }}, not {{ formatNode . }}{{end -}}`,
+		map[string]interface{}{"actual": actual})
+}
+
+func cmpErrorTypeEqualType(err error, expectedType reflect.Type) Result {
+	if err == nil {
+		return ResultFailure(fmt.Sprintf("error is nil, not %s", expectedType))
+	}
+	errValue := reflect.ValueOf(err)
+	if errValue.Type() == expectedType {
+		return ResultSuccess
+	}
+	return ResultFailure(fmt.Sprintf("error is %s (%T), not %s", err, err, expectedType))
+}
+
+func cmpErrorTypeImplementsType(err error, expectedType reflect.Type) Result {
+	if err == nil {
+		return ResultFailure(fmt.Sprintf("error is nil, not %s", expectedType))
+	}
+	errValue := reflect.ValueOf(err)
+	if errValue.Type().Implements(expectedType) {
+		return ResultSuccess
+	}
+	return ResultFailure(fmt.Sprintf("error is %s (%T), not %s", err, err, expectedType))
+}
+
+func isPtrToInterface(typ reflect.Type) bool {
+	return typ.Kind() == reflect.Ptr && typ.Elem().Kind() == reflect.Interface
+}
+
+func isPtrToStruct(typ reflect.Type) bool {
+	return typ.Kind() == reflect.Ptr && typ.Elem().Kind() == reflect.Struct
+}
diff --git a/vendor/gotest.tools/assert/cmp/result.go b/vendor/gotest.tools/assert/cmp/result.go
new file mode 100644
index 00000000..7c3c37dd
--- /dev/null
+++ b/vendor/gotest.tools/assert/cmp/result.go
@@ -0,0 +1,94 @@
+package cmp
+
+import (
+	"bytes"
+	"fmt"
+	"go/ast"
+	"text/template"
+
+	"gotest.tools/internal/source"
+)
+
+// Result of a Comparison.
+type Result interface {
+	Success() bool
+}
+
+type result struct {
+	success bool
+	message string
+}
+
+func (r result) Success() bool {
+	return r.success
+}
+
+func (r result) FailureMessage() string {
+	return r.message
+}
+
+// ResultSuccess is a constant which is returned by a ComparisonWithResult to
+// indicate success.
+var ResultSuccess = result{success: true}
+
+// ResultFailure returns a failed Result with a failure message.
+func ResultFailure(message string) Result {
+	return result{message: message}
+}
+
+// ResultFromError returns ResultSuccess if err is nil. Otherwise ResultFailure
+// is returned with the error message as the failure message.
+func ResultFromError(err error) Result {
+	if err == nil {
+		return ResultSuccess
+	}
+	return ResultFailure(err.Error())
+}
+
+type templatedResult struct {
+	success  bool
+	template string
+	data     map[string]interface{}
+}
+
+func (r templatedResult) Success() bool {
+	return r.success
+}
+
+func (r templatedResult) FailureMessage(args []ast.Expr) string {
+	msg, err := renderMessage(r, args)
+	if err != nil {
+		return fmt.Sprintf("failed to render failure message: %s", err)
+	}
+	return msg
+}
+
+// ResultFailureTemplate returns a Result with a template string and data which
+// can be used to format a failure message. The template may access data from .Data,
+// the comparison args with the callArg function, and the formatNode function may
+// be used to format the call args.
+func ResultFailureTemplate(template string, data map[string]interface{}) Result {
+	return templatedResult{template: template, data: data}
+}
+
+func renderMessage(result templatedResult, args []ast.Expr) (string, error) {
+	tmpl := template.New("failure").Funcs(template.FuncMap{
+		"formatNode": source.FormatNode,
+		"callArg": func(index int) ast.Expr {
+			if index >= len(args) {
+				return nil
+			}
+			return args[index]
+		},
+	})
+	var err error
+	tmpl, err = tmpl.Parse(result.template)
+	if err != nil {
+		return "", err
+	}
+	buf := new(bytes.Buffer)
+	err = tmpl.Execute(buf, map[string]interface{}{
+		"Data": result.data,
+	})
+	return buf.String(), err
+}
diff --git a/vendor/gotest.tools/assert/result.go b/vendor/gotest.tools/assert/result.go
new file mode 100644
index 00000000..3900264d
--- /dev/null
+++ b/vendor/gotest.tools/assert/result.go
@@ -0,0 +1,107 @@
+package assert
+
+import (
+	"fmt"
+	"go/ast"
+
+	"gotest.tools/assert/cmp"
+	"gotest.tools/internal/format"
+	"gotest.tools/internal/source"
+)
+
+func runComparison(
+	t TestingT,
+	argSelector argSelector,
+	f cmp.Comparison,
+	msgAndArgs ...interface{},
+) bool {
+	if ht, ok := t.(helperT); ok {
+		ht.Helper()
+	}
+	result := f()
+	if result.Success() {
+		return true
+	}
+
+	var message string
+	switch typed := result.(type) {
+	case resultWithComparisonArgs:
+		const stackIndex = 3 // Assert/Check, assert, runComparison
+		args, err := source.CallExprArgs(stackIndex)
+		if err != nil {
+			t.Log(err.Error())
+		}
+		message = typed.FailureMessage(filterPrintableExpr(argSelector(args)))
+	case resultBasic:
+		message = typed.FailureMessage()
+	default:
+		message = fmt.Sprintf("comparison returned invalid Result type: %T", result)
+	}
+
+	t.Log(format.WithCustomMessage(failureMessage+message, msgAndArgs...))
+	return false
+}
+
+type resultWithComparisonArgs interface {
+	FailureMessage(args []ast.Expr) string
+}
+
+type resultBasic interface {
+	FailureMessage() string
+}
+
+// filterPrintableExpr filters the ast.Expr slice to only include Expr that are
+// easy to read when printed and contain relevant information to an assertion.
+//
+// Ident and SelectorExpr are included because they print nicely and the variable
+// names may provide additional context to their values.
+// BasicLit and CompositeLit are excluded because their source is equivalent to
+// their value, which is already available.
+// Other types are ignored for now, but could be added if they are relevant.
+func filterPrintableExpr(args []ast.Expr) []ast.Expr {
+	result := make([]ast.Expr, len(args))
+	for i, arg := range args {
+		if isShortPrintableExpr(arg) {
+			result[i] = arg
+			continue
+		}
+
+		if starExpr, ok := arg.(*ast.StarExpr); ok {
+			result[i] = starExpr.X
+			continue
+		}
+		result[i] = nil
+	}
+	return result
+}
+
+func isShortPrintableExpr(expr ast.Expr) bool {
+	switch expr.(type) {
+	case *ast.Ident, *ast.SelectorExpr, *ast.IndexExpr, *ast.SliceExpr:
+		return true
+	case *ast.BinaryExpr, *ast.UnaryExpr:
+		return true
+	default:
+		// CallExpr, ParenExpr, TypeAssertExpr, KeyValueExpr, StarExpr
+		return false
+	}
+}
+
+type argSelector func([]ast.Expr) []ast.Expr
+
+func argsAfterT(args []ast.Expr) []ast.Expr {
+	if len(args) < 1 {
+		return nil
+	}
+	return args[1:]
+}
+
+func argsFromComparisonCall(args []ast.Expr) []ast.Expr {
+	if len(args) < 1 {
+		return nil
+	}
+	if callExpr, ok := args[1].(*ast.CallExpr); ok {
+		return callExpr.Args
+	}
+	return nil
+}
diff --git a/vendor/gotest.tools/internal/difflib/LICENSE b/vendor/gotest.tools/internal/difflib/LICENSE
new file mode 100644
index 00000000..c67dad61
--- /dev/null
+++ b/vendor/gotest.tools/internal/difflib/LICENSE
@@ -0,0 +1,27 @@
+Copyright (c) 2013, Patrick Mezard
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+    Redistributions of source code must retain the above copyright
+notice, this list of conditions and the following disclaimer.
+    Redistributions in binary form must reproduce the above copyright
+notice, this list of conditions and the following disclaimer in the
+documentation and/or other materials provided with the distribution.
+    The names of its contributors may not be used to endorse or promote
+products derived from this software without specific prior written
+permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
+IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
+PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
+TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/vendor/gotest.tools/internal/difflib/difflib.go b/vendor/gotest.tools/internal/difflib/difflib.go
new file mode 100644
index 00000000..5efa99c1
--- /dev/null
+++ b/vendor/gotest.tools/internal/difflib/difflib.go
@@ -0,0 +1,420 @@
+/* Package difflib is a partial port of Python difflib module.
+
+Original source: https://github.com/pmezard/go-difflib
+
+This file is trimmed to only the parts used by this repository.
+*/
+package difflib // import "gotest.tools/internal/difflib"
+
+func min(a, b int) int {
+	if a < b {
+		return a
+	}
+	return b
+}
+
+func max(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}
+
+type Match struct {
+	A    int
+	B    int
+	Size int
+}
+
+type OpCode struct {
+	Tag byte
+	I1  int
+	I2  int
+	J1  int
+	J2  int
+}
+
+// SequenceMatcher compares sequence of strings. The basic
+// algorithm predates, and is a little fancier than, an algorithm
+// published in the late 1980's by Ratcliff and Obershelp under the
+// hyperbolic name "gestalt pattern matching".  The basic idea is to find
+// the longest contiguous matching subsequence that contains no "junk"
+// elements (R-O doesn't address junk).  The same idea is then applied
+// recursively to the pieces of the sequences to the left and to the right
+// of the matching subsequence.  This does not yield minimal edit
+// sequences, but does tend to yield matches that "look right" to people.
+//
+// SequenceMatcher tries to compute a "human-friendly diff" between two
+// sequences.  Unlike e.g. UNIX(tm) diff, the fundamental notion is the
+// longest *contiguous* & junk-free matching subsequence.  That's what
+// catches peoples' eyes.  The Windows(tm) windiff has another interesting
+// notion, pairing up elements that appear uniquely in each sequence.
+// That, and the method here, appear to yield more intuitive difference
+// reports than does diff.  This method appears to be the least vulnerable
+// to synching up on blocks of "junk lines", though (like blank lines in
+// ordinary text files, or maybe "<P>" lines in HTML files).  That may be
+// because this is the only method of the 3 that has a *concept* of
+// "junk" <wink>.
+//
+// Timing:  Basic R-O is cubic time worst case and quadratic time expected
+// case.  SequenceMatcher is quadratic time for the worst case and has
+// expected-case behavior dependent in a complicated way on how many
+// elements the sequences have in common; best case time is linear.
+type SequenceMatcher struct {
+	a              []string
+	b              []string
+	b2j            map[string][]int
+	IsJunk         func(string) bool
+	autoJunk       bool
+	bJunk          map[string]struct{}
+	matchingBlocks []Match
+	fullBCount     map[string]int
+	bPopular       map[string]struct{}
+	opCodes        []OpCode
+}
+
+func NewMatcher(a, b []string) *SequenceMatcher {
+	m := SequenceMatcher{autoJunk: true}
+	m.SetSeqs(a, b)
+	return &m
+}
+
+// Set two sequences to be compared.
+func (m *SequenceMatcher) SetSeqs(a, b []string) {
+	m.SetSeq1(a)
+	m.SetSeq2(b)
+}
+
+// Set the first sequence to be compared. The second sequence to be compared is
+// not changed.
+//
+// SequenceMatcher computes and caches detailed information about the second
+// sequence, so if you want to compare one sequence S against many sequences,
+// use .SetSeq2(s) once and call .SetSeq1(x) repeatedly for each of the other
+// sequences.
+//
+// See also SetSeqs() and SetSeq2().
+func (m *SequenceMatcher) SetSeq1(a []string) {
+	if &a == &m.a {
+		return
+	}
+	m.a = a
+	m.matchingBlocks = nil
+	m.opCodes = nil
+}
+
+// Set the second sequence to be compared. The first sequence to be compared is
+// not changed.
+func (m *SequenceMatcher) SetSeq2(b []string) {
+	if &b == &m.b {
+		return
+	}
+	m.b = b
+	m.matchingBlocks = nil
+	m.opCodes = nil
+	m.fullBCount = nil
+	m.chainB()
+}
+
+func (m *SequenceMatcher) chainB() {
+	// Populate line -> index mapping
+	b2j := map[string][]int{}
+	for i, s := range m.b {
+		indices := b2j[s]
+		indices = append(indices, i)
+		b2j[s] = indices
+	}
+
+	// Purge junk elements
+	m.bJunk = map[string]struct{}{}
+	if m.IsJunk != nil {
+		junk := m.bJunk
+		for s, _ := range b2j {
+			if m.IsJunk(s) {
+				junk[s] = struct{}{}
+			}
+		}
+		for s, _ := range junk {
+			delete(b2j, s)
+		}
+	}
+
+	// Purge remaining popular elements
+	popular := map[string]struct{}{}
+	n := len(m.b)
+	if m.autoJunk && n >= 200 {
+		ntest := n/100 + 1
+		for s, indices := range b2j {
+			if len(indices) > ntest {
+				popular[s] = struct{}{}
+			}
+		}
+		for s, _ := range popular {
+			delete(b2j, s)
+		}
+	}
+	m.bPopular = popular
+	m.b2j = b2j
+}
+
+func (m *SequenceMatcher) isBJunk(s string) bool {
+	_, ok := m.bJunk[s]
+	return ok
+}
+
+// Find longest matching block in a[alo:ahi] and b[blo:bhi].
+//
+// If IsJunk is not defined:
+//
+// Return (i,j,k) such that a[i:i+k] is equal to b[j:j+k], where
+//     alo <= i <= i+k <= ahi
+//     blo <= j <= j+k <= bhi
+// and for all (i',j',k') meeting those conditions,
+//     k >= k'
+//     i <= i'
+//     and if i == i', j <= j'
+//
+// In other words, of all maximal matching blocks, return one that
+// starts earliest in a, and of all those maximal matching blocks that
+// start earliest in a, return the one that starts earliest in b.
+//
+// If IsJunk is defined, first the longest matching block is
+// determined as above, but with the additional restriction that no
+// junk element appears in the block.  Then that block is extended as
+// far as possible by matching (only) junk elements on both sides.  So
+// the resulting block never matches on junk except as identical junk
+// happens to be adjacent to an "interesting" match.
+//
+// If no blocks match, return (alo, blo, 0).
+func (m *SequenceMatcher) findLongestMatch(alo, ahi, blo, bhi int) Match {
+	// CAUTION:  stripping common prefix or suffix would be incorrect.
+	// E.g.,
+	//    ab
+	//    acab
+	// Longest matching block is "ab", but if common prefix is
+	// stripped, it's "a" (tied with "b").  UNIX(tm) diff does so
+	// strip, so ends up claiming that ab is changed to acab by
+	// inserting "ca" in the middle.  That's minimal but unintuitive:
+	// "it's obvious" that someone inserted "ac" at the front.
+	// Windiff ends up at the same place as diff, but by pairing up
+	// the unique 'b's and then matching the first two 'a's.
+	besti, bestj, bestsize := alo, blo, 0
+
+	// find longest junk-free match
+	// during an iteration of the loop, j2len[j] = length of longest
+	// junk-free match ending with a[i-1] and b[j]
+	j2len := map[int]int{}
+	for i := alo; i != ahi; i++ {
+		// look at all instances of a[i] in b; note that because
+		// b2j has no junk keys, the loop is skipped if a[i] is junk
+		newj2len := map[int]int{}
+		for _, j := range m.b2j[m.a[i]] {
+			// a[i] matches b[j]
+			if j < blo {
+				continue
+			}
+			if j >= bhi {
+				break
+			}
+			k := j2len[j-1] + 1
+			newj2len[j] = k
+			if k > bestsize {
+				besti, bestj, bestsize = i-k+1, j-k+1, k
+			}
+		}
+		j2len = newj2len
+	}
+
+	// Extend the best by non-junk elements on each end.  In particular,
+	// "popular" non-junk elements aren't in b2j, which greatly speeds
+	// the inner loop above, but also means "the best" match so far
+	// doesn't contain any junk *or* popular non-junk elements.
+	for besti > alo && bestj > blo && !m.isBJunk(m.b[bestj-1]) &&
+		m.a[besti-1] == m.b[bestj-1] {
+		besti, bestj, bestsize = besti-1, bestj-1, bestsize+1
+	}
+	for besti+bestsize < ahi && bestj+bestsize < bhi &&
+		!m.isBJunk(m.b[bestj+bestsize]) &&
+		m.a[besti+bestsize] == m.b[bestj+bestsize] {
+		bestsize += 1
+	}
+
+	// Now that we have a wholly interesting match (albeit possibly
+	// empty!), we may as well suck up the matching junk on each
+	// side of it too.  Can't think of a good reason not to, and it
+	// saves post-processing the (possibly considerable) expense of
+	// figuring out what to do with it.  In the case of an empty
+	// interesting match, this is clearly the right thing to do,
+	// because no other kind of match is possible in the regions.
+	for besti > alo && bestj > blo && m.isBJunk(m.b[bestj-1]) &&
+		m.a[besti-1] == m.b[bestj-1] {
+		besti, bestj, bestsize = besti-1, bestj-1, bestsize+1
+	}
+	for besti+bestsize < ahi && bestj+bestsize < bhi &&
+		m.isBJunk(m.b[bestj+bestsize]) &&
+		m.a[besti+bestsize] == m.b[bestj+bestsize] {
+		bestsize += 1
+	}
+
+	return Match{A: besti, B: bestj, Size: bestsize}
+}
+
+// Return list of triples describing matching subsequences.
+//
+// Each triple is of the form (i, j, n), and means that
+// a[i:i+n] == b[j:j+n].  The triples are monotonically increasing in
+// i and in j. It's also guaranteed that if (i, j, n) and (i', j', n') are
+// adjacent triples in the list, and the second is not the last triple in the
+// list, then i+n != i' or j+n != j'. IOW, adjacent triples never describe
+// adjacent equal blocks.
+//
+// The last triple is a dummy, (len(a), len(b), 0), and is the only
+// triple with n==0.
+func (m *SequenceMatcher) GetMatchingBlocks() []Match {
+	if m.matchingBlocks != nil {
+		return m.matchingBlocks
+	}
+
+	var matchBlocks func(alo, ahi, blo, bhi int, matched []Match) []Match
+	matchBlocks = func(alo, ahi, blo, bhi int, matched []Match) []Match {
+		match := m.findLongestMatch(alo, ahi, blo, bhi)
+		i, j, k := match.A, match.B, match.Size
+		if match.Size > 0 {
+			if alo < i && blo < j {
+				matched = matchBlocks(alo, i, blo, j, matched)
+			}
+			matched = append(matched, match)
+			if i+k < ahi && j+k < bhi {
+				matched = matchBlocks(i+k, ahi, j+k, bhi, matched)
+			}
+		}
+		return matched
+	}
+	matched := matchBlocks(0, len(m.a), 0, len(m.b), nil)
+
+	// It's possible that we have adjacent equal blocks in the
+	// matching_blocks list now.
+	nonAdjacent := []Match{}
+	i1, j1, k1 := 0, 0, 0
+	for _, b := range matched {
+		// Is this block adjacent to i1, j1, k1?
+		i2, j2, k2 := b.A, b.B, b.Size
+		if i1+k1 == i2 && j1+k1 == j2 {
+			// Yes, so collapse them -- this just increases the length of
+			// the first block by the length of the second, and the first
+			// block so lengthened remains the block to compare against.
+			k1 += k2
+		} else {
+			// Not adjacent.  Remember the first block (k1==0 means it's
+			// the dummy we started with), and make the second block the
+			// new block to compare against.
+			if k1 > 0 {
+				nonAdjacent = append(nonAdjacent, Match{i1, j1, k1})
+			}
+			i1, j1, k1 = i2, j2, k2
+		}
+	}
+	if k1 > 0 {
+		nonAdjacent = append(nonAdjacent, Match{i1, j1, k1})
+	}
+
+	nonAdjacent = append(nonAdjacent, Match{len(m.a), len(m.b), 0})
+	m.matchingBlocks = nonAdjacent
+	return m.matchingBlocks
+}
+
+// Return list of 5-tuples describing how to turn a into b.
+//
+// Each tuple is of the form (tag, i1, i2, j1, j2).  The first tuple
+// has i1 == j1 == 0, and remaining tuples have i1 == the i2 from the
+// tuple preceding it, and likewise for j1 == the previous j2.
+//
+// The tags are characters, with these meanings:
+//
+// 'r' (replace):  a[i1:i2] should be replaced by b[j1:j2]
+//
+// 'd' (delete):   a[i1:i2] should be deleted, j1==j2 in this case.
+//
+// 'i' (insert):   b[j1:j2] should be inserted at a[i1:i1], i1==i2 in this case.
+//
+// 'e' (equal):    a[i1:i2] == b[j1:j2]
+func (m *SequenceMatcher) GetOpCodes() []OpCode {
+	if m.opCodes != nil {
+		return m.opCodes
+	}
+	i, j := 0, 0
+	matching := m.GetMatchingBlocks()
+	opCodes := make([]OpCode, 0, len(matching))
+	for _, m := range matching {
+		//  invariant:  we've pumped out correct diffs to change
+		//  a[:i] into b[:j], and the next matching block is
+		//  a[ai:ai+size] == b[bj:bj+size]. So we need to pump
+		//  out a diff to change a[i:ai] into b[j:bj], pump out
+		//  the matching block, and move (i,j) beyond the match
+		ai, bj, size := m.A, m.B, m.Size
+		tag := byte(0)
+		if i < ai && j < bj {
+			tag = 'r'
+		} else if i < ai {
+			tag = 'd'
+		} else if j < bj {
+			tag = 'i'
+		}
+		if tag > 0 {
+			opCodes = append(opCodes, OpCode{tag, i, ai, j, bj})
+		}
+		i, j = ai+size, bj+size
+		// the list of matching blocks is terminated by a
+		// sentinel with size 0
+		if size > 0 {
+			opCodes = append(opCodes, OpCode{'e', ai, i, bj, j})
+		}
+	}
+	m.opCodes = opCodes
+	return m.opCodes
+}
+
+// Isolate change clusters by eliminating ranges with no changes.
+//
+// Return a generator of groups with up to n lines of context.
+// Each group is in the same format as returned by GetOpCodes().
+func (m *SequenceMatcher) GetGroupedOpCodes(n int) [][]OpCode {
+	if n < 0 {
+		n = 3
+	}
+	codes := m.GetOpCodes()
+	if len(codes) == 0 {
+		codes = []OpCode{OpCode{'e', 0, 1, 0, 1}}
+	}
+	// Fixup leading and trailing groups if they show no changes.
+	if codes[0].Tag == 'e' {
+		c := codes[0]
+		i1, i2, j1, j2 := c.I1, c.I2, c.J1, c.J2
+		codes[0] = OpCode{c.Tag, max(i1, i2-n), i2, max(j1, j2-n), j2}
+	}
+	if codes[len(codes)-1].Tag == 'e' {
+		c := codes[len(codes)-1]
+		i1, i2, j1, j2 := c.I1, c.I2, c.J1, c.J2
+		codes[len(codes)-1] = OpCode{c.Tag, i1, min(i2, i1+n), j1, min(j2, j1+n)}
+	}
+	nn := n + n
+	groups := [][]OpCode{}
+	group := []OpCode{}
+	for _, c := range codes {
+		i1, i2, j1, j2 := c.I1, c.I2, c.J1, c.J2
+		// End the current group and start a new one whenever
+		// there is a large range with no changes.
+		if c.Tag == 'e' && i2-i1 > nn {
+			group = append(group, OpCode{c.Tag, i1, min(i2, i1+n),
+				j1, min(j2, j1+n)})
+			groups = append(groups, group)
+			group = []OpCode{}
+			i1, j1 = max(i1, i2-n), max(j1, j2-n)
+		}
+		group = append(group, OpCode{c.Tag, i1, i2, j1, j2})
+	}
+	if len(group) > 0 && !(len(group) == 1 && group[0].Tag == 'e') {
+		groups = append(groups, group)
+	}
+	return groups
+}
diff --git a/vendor/gotest.tools/internal/format/diff.go b/vendor/gotest.tools/internal/format/diff.go
new file mode 100644
index 00000000..c938c97b
--- /dev/null
+++ b/vendor/gotest.tools/internal/format/diff.go
@@ -0,0 +1,161 @@
+package format
+
+import (
+	"bytes"
+	"fmt"
+	"strings"
+	"unicode"
+
+	"gotest.tools/internal/difflib"
+)
+
+const (
+	contextLines = 2
+)
+
+// DiffConfig for a unified diff
+type DiffConfig struct {
+	A    string
+	B    string
+	From string
+	To   string
+}
+
+// UnifiedDiff is a modified version of difflib.WriteUnifiedDiff with better
+// support for showing the whitespace differences.
+func UnifiedDiff(conf DiffConfig) string {
+	a := strings.SplitAfter(conf.A, "\n")
+	b := strings.SplitAfter(conf.B, "\n")
+	groups := difflib.NewMatcher(a, b).GetGroupedOpCodes(contextLines)
+	if len(groups) == 0 {
+		return ""
+	}
+
+	buf := new(bytes.Buffer)
+	writeFormat := func(format string, args ...interface{}) {
+		buf.WriteString(fmt.Sprintf(format, args...))
+	}
+	writeLine := func(prefix string, s string) {
+		buf.WriteString(prefix + s)
+	}
+	if hasWhitespaceDiffLines(groups, a, b) {
+		writeLine = visibleWhitespaceLine(writeLine)
+	}
+	formatHeader(writeFormat, conf)
+	for _, group := range groups {
+		formatRangeLine(writeFormat, group)
+		for _, opCode := range group {
+			in, out := a[opCode.I1:opCode.I2], b[opCode.J1:opCode.J2]
+			switch opCode.Tag {
+			case 'e':
+				formatLines(writeLine, " ", in)
+			case 'r':
+				formatLines(writeLine, "-", in)
+				formatLines(writeLine, "+", out)
+			case 'd':
+				formatLines(writeLine, "-", in)
+			case 'i':
+				formatLines(writeLine, "+", out)
+			}
+		}
+	}
+	return buf.String()
+}
+
+// hasWhitespaceDiffLines returns true if any diff groups is only different
+// because of whitespace characters.
+func hasWhitespaceDiffLines(groups [][]difflib.OpCode, a, b []string) bool {
+	for _, group := range groups {
+		in, out := new(bytes.Buffer), new(bytes.Buffer)
+		for _, opCode := range group {
+			if opCode.Tag == 'e' {
+				continue
+			}
+			for _, line := range a[opCode.I1:opCode.I2] {
+				in.WriteString(line)
+			}
+			for _, line := range b[opCode.J1:opCode.J2] {
+				out.WriteString(line)
+			}
+		}
+		if removeWhitespace(in.String()) == removeWhitespace(out.String()) {
+			return true
+		}
+	}
+	return false
+}
+
+func removeWhitespace(s string) string {
+	var result []rune
+	for _, r := range s {
+		if !unicode.IsSpace(r) {
+			result = append(result, r)
+		}
+	}
+	return string(result)
+}
+
+func visibleWhitespaceLine(ws func(string, string)) func(string, string) {
+	mapToVisibleSpace := func(r rune) rune {
+		switch r {
+		case '\n':
+		case ' ':
+			return '·'
+		case '\t':
+			return '▷'
+		case '\v':
+			return '▽'
+		case '\r':
+			return '↵'
+		case '\f':
+			return '↓'
+		default:
+			if unicode.IsSpace(r) {
+				return '�'
+			}
+		}
+		return r
+	}
+	return func(prefix, s string) {
+		ws(prefix, strings.Map(mapToVisibleSpace, s))
+	}
+}
+
+func formatHeader(wf func(string, ...interface{}), conf DiffConfig) {
+	if conf.From != "" || conf.To != "" {
+		wf("--- %s\n", conf.From)
+		wf("+++ %s\n", conf.To)
+	}
+}
+
+func formatRangeLine(wf func(string, ...interface{}), group []difflib.OpCode) {
+	first, last := group[0], group[len(group)-1]
+	range1 := formatRangeUnified(first.I1, last.I2)
+	range2 := formatRangeUnified(first.J1, last.J2)
+	wf("@@ -%s +%s @@\n", range1, range2)
+}
+
+// Convert range to the "ed" format
+func formatRangeUnified(start, stop int) string {
+	// Per the diff spec at http://www.unix.org/single_unix_specification/
+	beginning := start + 1 // lines start numbering with one
+	length := stop - start
+	if length == 1 {
+		return fmt.Sprintf("%d", beginning)
+	}
+	if length == 0 {
+		beginning-- // empty ranges begin at line just before the range
+	}
+	return fmt.Sprintf("%d,%d", beginning, length)
+}
+
+func formatLines(writeLine func(string, string), prefix string, lines []string) {
+	for _, line := range lines {
+		writeLine(prefix, line)
+	}
+	// Add a newline if the last line is missing one so that the diff displays
+	// properly.
+	if !strings.HasSuffix(lines[len(lines)-1], "\n") {
+		writeLine("", "\n")
+	}
+}
diff --git a/vendor/gotest.tools/internal/format/format.go b/vendor/gotest.tools/internal/format/format.go
new file mode 100644
index 00000000..8f6494f9
--- /dev/null
+++ b/vendor/gotest.tools/internal/format/format.go
@@ -0,0 +1,27 @@
+package format // import "gotest.tools/internal/format"
+
+import "fmt"
+
+// Message accepts a msgAndArgs varargs and formats it using fmt.Sprintf
+func Message(msgAndArgs ...interface{}) string {
+	switch len(msgAndArgs) {
+	case 0:
+		return ""
+	case 1:
+		return fmt.Sprintf("%v", msgAndArgs[0])
+	default:
+		return fmt.Sprintf(msgAndArgs[0].(string), msgAndArgs[1:]...)
+	}
+}
+
+// WithCustomMessage accepts one or two messages and formats them appropriately
+func WithCustomMessage(source string, msgAndArgs ...interface{}) string {
+	custom := Message(msgAndArgs...)
+	switch {
+	case custom == "":
+		return source
+	case source == "":
+		return custom
+	}
+	return fmt.Sprintf("%s: %s", source, custom)
+}
diff --git a/vendor/gotest.tools/internal/source/source.go b/vendor/gotest.tools/internal/source/source.go
new file mode 100644
index 00000000..a05933cc
--- /dev/null
+++ b/vendor/gotest.tools/internal/source/source.go
@@ -0,0 +1,163 @@
+package source // import "gotest.tools/internal/source"
+
+import (
+	"bytes"
+	"fmt"
+	"go/ast"
+	"go/format"
+	"go/parser"
+	"go/token"
+	"os"
+	"runtime"
+	"strconv"
+	"strings"
+
+	"github.com/pkg/errors"
+)
+
+const baseStackIndex = 1
+
+// FormattedCallExprArg returns the argument from an ast.CallExpr at the
+// index in the call stack. The argument is formatted using FormatNode.
+func FormattedCallExprArg(stackIndex int, argPos int) (string, error) {
+	args, err := CallExprArgs(stackIndex + 1)
+	if err != nil {
+		return "", err
+	}
+	return FormatNode(args[argPos])
+}
+
+func getNodeAtLine(filename string, lineNum int) (ast.Node, error) {
+	fileset := token.NewFileSet()
+	astFile, err := parser.ParseFile(fileset, filename, nil, parser.AllErrors)
+	if err != nil {
+		return nil, errors.Wrapf(err, "failed to parse source file: %s", filename)
+	}
+
+	node := scanToLine(fileset, astFile, lineNum)
+	if node == nil {
+		return nil, errors.Errorf(
+			"failed to find an expression on line %d in %s", lineNum, filename)
+	}
+	return node, nil
+}
+
+func scanToLine(fileset *token.FileSet, node ast.Node, lineNum int) ast.Node {
+	v := &scanToLineVisitor{lineNum: lineNum, fileset: fileset}
+	ast.Walk(v, node)
+	return v.matchedNode
+}
+
+type scanToLineVisitor struct {
+	lineNum     int
+	matchedNode ast.Node
+	fileset     *token.FileSet
+}
+
+func (v *scanToLineVisitor) Visit(node ast.Node) ast.Visitor {
+	if node == nil || v.matchedNode != nil {
+		return nil
+	}
+	if v.nodePosition(node).Line == v.lineNum {
+		v.matchedNode = node
+		return nil
+	}
+	return v
+}
+
+// In golang 1.9 the line number changed from being the line where the statement
+// ended to the line where the statement began.
+func (v *scanToLineVisitor) nodePosition(node ast.Node) token.Position {
+	if goVersionBefore19 {
+		return v.fileset.Position(node.End())
+	}
+	return v.fileset.Position(node.Pos())
+}
+
+var goVersionBefore19 = isGOVersionBefore19()
+
+func isGOVersionBefore19() bool {
+	version := runtime.Version()
+	// not a release version
+	if !strings.HasPrefix(version, "go") {
+		return false
+	}
+	version = strings.TrimPrefix(version, "go")
+	parts := strings.Split(version, ".")
+	if len(parts) < 2 {
+		return false
+	}
+	minor, err := strconv.ParseInt(parts[1], 10, 32)
+	return err == nil && parts[0] == "1" && minor < 9
+}
+
+func getCallExprArgs(node ast.Node) ([]ast.Expr, error) {
+	visitor := &callExprVisitor{}
+	ast.Walk(visitor, node)
+	if visitor.expr == nil {
+		return nil, errors.New("failed to find call expression")
+	}
+	return visitor.expr.Args, nil
+}
+
+type callExprVisitor struct {
+	expr *ast.CallExpr
+}
+
+func (v *callExprVisitor) Visit(node ast.Node) ast.Visitor {
+	if v.expr != nil || node == nil {
+		return nil
+	}
+	debug("visit (%T): %s", node, debugFormatNode{node})
+
+	if callExpr, ok := node.(*ast.CallExpr); ok {
+		v.expr = callExpr
+		return nil
+	}
+	return v
+}
+
+// FormatNode using go/format.Node and return the result as a string
+func FormatNode(node ast.Node) (string, error) {
+	buf := new(bytes.Buffer)
+	err := format.Node(buf, token.NewFileSet(), node)
+	return buf.String(), err
+}
+
+// CallExprArgs returns the ast.Expr slice for the args of an ast.CallExpr at
+// the index in the call stack.
+func CallExprArgs(stackIndex int) ([]ast.Expr, error) {
+	_, filename, lineNum, ok := runtime.Caller(baseStackIndex + stackIndex)
+	if !ok {
+		return nil, errors.New("failed to get call stack")
+	}
+	debug("call stack position: %s:%d", filename, lineNum)
+
+	node, err := getNodeAtLine(filename, lineNum)
+	if err != nil {
+		return nil, err
+	}
+	debug("found node (%T): %s", node, debugFormatNode{node})
+
+	return getCallExprArgs(node)
+}
+
+var debugEnabled = os.Getenv("GOTESTYOURSELF_DEBUG") != ""
+
+func debug(format string, args ...interface{}) {
+	if debugEnabled {
+		fmt.Fprintf(os.Stderr, "DEBUG: "+format+"\n", args...)
+	}
+}
+
+type debugFormatNode struct {
+	ast.Node
+}
+
+func (n debugFormatNode) String() string {
+	out, err := FormatNode(n.Node)
+	if err != nil {
+		return fmt.Sprintf("failed to format %s: %s", n.Node, err)
+	}
+	return out
+}