assert: Add Error and ErrorContains

Author: nhooyr

Diff for: sloggers/slogtest/assert/assert.go

@@ -1,7 +1,12 @@
 // Package assert is a helper package for test assertions.
+//
+// On failure, every assertion will fatal the test.
+//
+// The name parameter is available in each assertion for easier debugging.
 package assert // import "cdr.dev/slog/sloggers/slogtest/assert"
 
 import (
+	"errors"
 	"testing"
 
 	"cdr.dev/slog"
@@ -13,8 +18,15 @@ import (
 //
 // If they are not equal, it will fatal the test with a diff of the
 // two objects.
+//
+// If act is an error it will be unwrapped.
 func Equal(t testing.TB, exp, act interface{}, name string) {
 	slog.Helper()
+
+	if err, ok := act.(error); ok {
+		act = unwrapErr(err)
+	}
+
 	if diff := assert.CmpDiff(exp, act); diff != "" {
 		slogtest.Fatal(t, "unexpected value",
 			slog.F("name", name),
@@ -24,8 +36,6 @@ func Equal(t testing.TB, exp, act interface{}, name string) {
 }
 
 // Success asserts err == nil.
-//
-// If err isn't nil, it will fatal the test with the error.
 func Success(t testing.TB, err error, name string) {
 	slog.Helper()
 	if err != nil {
@@ -37,9 +47,26 @@ func Success(t testing.TB, err error, name string) {
 }
 
 // True asserts act == true.
-//
-// If act isn't true, it will fatal the test.
 func True(t testing.TB, act bool, name string) {
 	slog.Helper()
 	Equal(t, true, act, name)
 }
+
+// Error asserts err != nil.
+func Error(t testing.TB, err error, name string) {
+	slog.Helper()
+	if err == nil {
+		slogtest.Fatal(t, "expected error",
+			slog.F("name", name),
+		)
+	}
+}
+
+func unwrapErr(err error) error {
+	uerr := errors.Unwrap(err)
+	for uerr != nil {
+		err = uerr
+		uerr = errors.Unwrap(uerr)
+	}
+	return err
+}

Diff for: sloggers/slogtest/assert/assert_test.go

@@ -1,6 +1,7 @@
 package assert_test
 
 import (
+	"fmt"
 	"io"
 	"testing"
 
@@ -21,6 +22,19 @@ func TestEqual(t *testing.T) {
 	assert.Equal(tb, 3, 4, "meow")
 }
 
+func TestEqual_error(t *testing.T) {
+	t.Parallel()
+
+	tb := &fakeTB{}
+	assert.Equal(tb, io.EOF, fmt.Errorf("failed: %w", io.EOF), "meow")
+
+	defer func() {
+		recover()
+		simpleassert.Equal(t, 1, tb.fatals, "fatals")
+	}()
+	assert.Equal(tb, io.ErrClosedPipe, fmt.Errorf("failed: %w", io.EOF), "meow")
+}
+
 func TestSuccess(t *testing.T) {
 	t.Parallel()
 
@@ -47,6 +61,19 @@ func TestTrue(t *testing.T) {
 	assert.True(tb, false, "meow")
 }
 
+func TestError(t *testing.T) {
+	t.Parallel()
+
+	tb := &fakeTB{}
+	assert.Error(tb, io.EOF, "meow")
+
+	defer func() {
+		recover()
+		simpleassert.Equal(t, 1, tb.fatals, "fatals")
+	}()
+	assert.Error(tb, nil, "meow")
+}
+
 type fakeTB struct {
 	testing.TB