[release-0.17] ⚠ 🐛 Fakeclient: Do not consider an apply patch to be a strategic merge patch

pkg/client/fake/client.go

@@ -947,16 +947,18 @@ func dryPatch(action testing.PatchActionImpl, tracker testing.ObjectTracker) (ru
 		if err := json.Unmarshal(modified, obj); err != nil {
 			return nil, err
 		}
-	case types.StrategicMergePatchType, types.ApplyPatchType:
+	case types.StrategicMergePatchType:
 		mergedByte, err := strategicpatch.StrategicMergePatch(old, action.GetPatch(), obj)
 		if err != nil {
 			return nil, err
 		}
 		if err = json.Unmarshal(mergedByte, obj); err != nil {
 			return nil, err
 		}
+	case types.ApplyPatchType:
+		return nil, errors.New("apply patches are not supported in the fake client. Follow https://github.com/kubernetes/kubernetes/issues/115598 for the current status")
 	default:
-		return nil, fmt.Errorf("PatchType is not supported")
+		return nil, fmt.Errorf("%s PatchType is not supported", action.GetPatchType())
 	}
 	return obj, nil
 }

pkg/client/fake/client_test.go

@@ -359,6 +359,26 @@ var _ = Describe("Fake client", func() {
 			Expect(list.Items).To(ConsistOf(*dep2))
 		})
 
+		It("should reject apply patches, they are not supported in the fake client", func() {
+			By("Creating a new configmap")
+			cm := &corev1.ConfigMap{
+				TypeMeta: metav1.TypeMeta{
+					APIVersion: "v1",
+					Kind:       "ConfigMap",
+				},
+				ObjectMeta: metav1.ObjectMeta{
+					Name:      "new-test-cm",
+					Namespace: "ns2",
+				},
+			}
+			err := cl.Create(context.Background(), cm)
+			Expect(err).ToNot(HaveOccurred())
+
+			cm.Data = map[string]string{"foo": "bar"}
+			err = cl.Patch(context.Background(), cm, client.Apply, client.ForceOwnership)
+			Expect(err).To(MatchError(ContainSubstring("apply patches are not supported in the fake client")))
+		})
+
 		It("should be able to Create", func() {
 			By("Creating a new configmap")
 			newcm := &corev1.ConfigMap{