Support errors.Unwrap and errors.Is (#194)

v2/errors/error_unwrap.go

@@ -0,0 +1,12 @@
+// +build go1.13
+
+package errors
+
+import (
+	"github.com/pkg/errors"
+)
+
+// Unwrap returns the result of calling errors.Unwrap on the underlying error
+func (err *Error) Unwrap() error {
+	return errors.Unwrap(err.Err)
+}

v2/errors/error_unwrap_test.go

@@ -0,0 +1,32 @@
+// +build go1.13
+
+package errors
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/pkg/errors"
+)
+
+func TestFindingErrorInChain(t *testing.T) {
+	baseErr := errors.New("base error")
+	wrappedErr := errors.Wrap(baseErr, "failed")
+	err := New(wrappedErr, 0)
+
+	if !errors.Is(err, baseErr) {
+		t.Errorf("Failed to find base error: %s", err.Error())
+	}
+}
+
+func TestErrorUnwrapping(t *testing.T) {
+	baseErr := errors.New("base error")
+	wrappedErr := fmt.Errorf("failed: %w", baseErr)
+	err := New(wrappedErr, 0)
+
+	unwrapped := errors.Unwrap(err)
+
+	if unwrapped != baseErr {
+		t.Errorf("Failed to find base error: %s", unwrapped.Error())
+	}
+}