Add a validation helper function.

I will use this in a subsequent PR as part of #12298

pkg/api/validation/validation_test.go

@@ -5009,3 +5009,40 @@ func TestValidateConfigMapUpdate(t *testing.T) {
 		}
 	}
 }
+
+func TestValidateHasLabel(t *testing.T) {
+	successCase := api.ObjectMeta{
+		Name:      "123",
+		Namespace: "ns",
+		Labels: map[string]string{
+			"other": "blah",
+			"foo":   "bar",
+		},
+	}
+	if errs := ValidateHasLabel(successCase, field.NewPath("field"), "foo", "bar"); len(errs) != 0 {
+		t.Errorf("expected success: %v", errs)
+	}
+
+	missingCase := api.ObjectMeta{
+		Name:      "123",
+		Namespace: "ns",
+		Labels: map[string]string{
+			"other": "blah",
+		},
+	}
+	if errs := ValidateHasLabel(missingCase, field.NewPath("field"), "foo", "bar"); len(errs) == 0 {
+		t.Errorf("expected failure")
+	}
+
+	wrongValueCase := api.ObjectMeta{
+		Name:      "123",
+		Namespace: "ns",
+		Labels: map[string]string{
+			"other": "blah",
+			"foo":   "notbar",
+		},
+	}
+	if errs := ValidateHasLabel(wrongValueCase, field.NewPath("field"), "foo", "bar"); len(errs) == 0 {
+		t.Errorf("expected failure")
+	}
+}