Negative index regression test for json-patch (#122625)

* add testcase with negative index

* exercise successful negative index patching

* use different values for testing

Co-authored-by: Chris Bandy <bandy.chris@gmail.com>

---------

Co-authored-by: Chris Bandy <bandy.chris@gmail.com>

staging/src/k8s.io/apiserver/pkg/endpoints/handlers/rest_test.go

@@ -244,6 +244,10 @@ func TestJSONPatch(t *testing.T) {
 			expectedError:     "the server rejected our request due to an error in our request",
 			expectedErrorType: metav1.StatusReasonInvalid,
 		},
+		{
+			name:  "valid-negative-index-patch",
+			patch: `[{"op": "test", "value": "foo", "path": "/metadata/finalizers/-1"}]`,
+		},
 	} {
 		p := &patcher{
 			patchType:  types.JSONPatchType,
@@ -253,6 +257,7 @@ func TestJSONPatch(t *testing.T) {
 		codec := codecs.LegacyCodec(examplev1.SchemeGroupVersion)
 		pod := &examplev1.Pod{}
 		pod.Name = "podA"
+		pod.ObjectMeta.Finalizers = []string{"foo"}
 		versionedJS, err := runtime.Encode(codec, pod)
 		if err != nil {
 			t.Errorf("%s: unexpected error: %v", test.name, err)

staging/src/k8s.io/kubectl/pkg/cmd/util/helpers_test.go

@@ -289,6 +289,26 @@ func TestJSONPatch(t *testing.T) {
 			fragment:  `[ {"op": "add", "path": "/metadata/labels/foo", "value": "bar"} ]`,
 			expectErr: true,
 		},
+		{
+			obj: &corev1.Pod{
+				ObjectMeta: metav1.ObjectMeta{
+					Name:       "foo",
+					Finalizers: []string{"foo", "bar", "test"},
+				},
+			},
+			fragment: `[ {"op": "replace", "path": "/metadata/finalizers/-1", "value": "baz"} ]`,
+			expected: &corev1.Pod{
+				TypeMeta: metav1.TypeMeta{
+					Kind:       "Pod",
+					APIVersion: "v1",
+				},
+				ObjectMeta: metav1.ObjectMeta{
+					Name:       "foo",
+					Finalizers: []string{"foo", "bar", "baz"},
+				},
+				Spec: corev1.PodSpec{},
+			},
+		},
 	}
 
 	codec := runtime.NewCodec(scheme.DefaultJSONEncoder(),