1 files changed, 43 insertions, 0 deletions
diff --git a/internal/test/checkers.go b/internal/test/checkers.go
new file mode 100644
index 0000000..257d93d
--- /dev/null
+++ b/internal/test/checkers.go
@@ -0,0 +1,43 @@
+package test
+
+import (
+	"errors"
+	"fmt"
+
+	check "gopkg.in/check.v1"
+)
+
+// This check.Checker implementation exists because there's no implementation
+// in the library that compares errors using `errors.Is`. If / when the check
+// library fixes https://github.com/go-check/check/issues/139, this code can
+// likely be removed and replaced with the library implementation.
+//
+// Added in Go 1.13 [https://go.dev/blog/go1.13-errors] `errors.Is` is the
+// best mechanism to use to compare errors that might be wrapped in other
+// errors.
+type errorIsChecker struct {
+	*check.CheckerInfo
+}
+
+var ErrorIs check.Checker = errorIsChecker{
+	&check.CheckerInfo{
+		Name:   "ErrorIs",
+		Params: []string{"obtained", "expected"},
+	},
+}
+
+func (e errorIsChecker) Check(params []interface{}, names []string) (bool, string) {
+	obtained, ok := params[0].(error)
+	if !ok {
+		return false, "obtained is not an error"
+	}
+	expected, ok := params[1].(error)
+	if !ok {
+		return false, "expected is not an error"
+	}
+
+	if !errors.Is(obtained, expected) {
+		return false, fmt.Sprintf("obtained: %+v expected: %+v", obtained, expected)
+	}
+	return true, ""
+}