Add WithUpdateEnv option to protect fixtures from blanket updates

Author: abiduke612

testutil/golden.go

@@ -29,6 +29,7 @@ func CompareWithFixture(t *testing.T, output interface{}, opts ...option) string
 	t.Helper()
 	options := &options{
 		Extension: ".yaml",
+		UpdateEnv: "UPDATE",
 	}
 	for _, opt := range opts {
 		opt(options)
@@ -52,7 +53,7 @@ func CompareWithFixture(t *testing.T, output interface{}, opts ...option) string
 	if err != nil {
 		t.Fatalf("failed to get absolute path to testdata file: %v", err)
 	}
-	if os.Getenv("UPDATE") != "" {
+	if os.Getenv(options.UpdateEnv) != "" {
 		if err := os.MkdirAll(filepath.Dir(golden), 0755); err != nil {
 			t.Fatalf("failed to create fixture directory: %v", err)
 		}
@@ -77,7 +78,8 @@ type options struct {
 	Suffix    string
 	Extension string
 
-	SubDir string
+	SubDir    string
+	UpdateEnv string
 }
 
 type option func(*options)
@@ -100,6 +102,12 @@ func WithSubDir(subDir string) option {
 	}
 }
 
+func WithUpdateEnv(env string) option {
+	return func(opts *options) {
+		opts.UpdateEnv = env
+	}
+}
+
 // golden determines the golden file to use
 func golden(t *testing.T, opts *options) (string, error) {
 	if opts.Extension == "" {