Play nicely with third-party testing libraries

See e.g. https://onsi.github.io/ginkgo/#using-third-party-libraries for a
use case of this setup.

Author: tomasaschan

pkg/test/golden/validator.go

@@ -25,7 +25,6 @@ import (
 	"os/exec"
 	"path/filepath"
 	"strings"
-	"testing"
 
 	"k8s.io/apimachinery/pkg/api/meta"
 	"k8s.io/apimachinery/pkg/runtime"
@@ -44,7 +43,25 @@ import (
 	"sigs.k8s.io/kustomize/kyaml/filesys"
 )
 
-func NewValidator(t *testing.T, b *scheme.Builder) *validator {
+// T re-exposes the parts of testing.T we're using as an interface,
+// in order to play more nicely with third-party libraries (e.g. gomega).
+// This helps making these testing utils compatible with the testing strategy
+// generated by kubebuilder.
+//
+// Note that testing.T has a bunch of other things as well; these are just the
+// ones currently in use in this project.
+//
+// See e.g. https://github.com/onsi/ginkgo/blob/master/ginkgo_t_dsl.go#L7-L17
+type T interface {
+	Cleanup(func())
+	Errorf(format string, args ...interface{})
+	Fatalf(format string, args ...interface{})
+	Helper()
+	Logf(format string, args ...interface{})
+	TempDir() string
+}
+
+func NewValidator(t T, b *scheme.Builder) *validator {
 	v := &validator{T: t, scheme: runtime.NewScheme()}
 	if err := b.AddToScheme(v.scheme); err != nil {
 		t.Fatalf("error from AddToScheme: %v", err)
@@ -87,7 +104,7 @@ func NewValidator(t *testing.T, b *scheme.Builder) *validator {
 }
 
 type validator struct {
-	T       *testing.T
+	T       T
 	scheme  *runtime.Scheme
 	TestDir string
 
@@ -351,7 +368,7 @@ func (v *validator) Validate(r declarative.Reconciler) {
 	}
 }
 
-func diffFiles(t *testing.T, expectedPath, actual string) error {
+func diffFiles(t T, expectedPath, actual string) error {
 	t.Helper()
 	writeTmp := func(content string) (string, error) {
 		tmp, err := os.CreateTemp("", "*.yaml")