add Patch support in fake kubeClient

staging/src/k8s.io/client-go/testing/BUILD

@@ -22,6 +22,8 @@ go_library(
         "//vendor/k8s.io/apimachinery/pkg/labels:go_default_library",
         "//vendor/k8s.io/apimachinery/pkg/runtime:go_default_library",
         "//vendor/k8s.io/apimachinery/pkg/runtime/schema:go_default_library",
+        "//vendor/k8s.io/apimachinery/pkg/util/json:go_default_library",
+        "//vendor/k8s.io/apimachinery/pkg/util/strategicpatch:go_default_library",
         "//vendor/k8s.io/apimachinery/pkg/watch:go_default_library",
         "//vendor/k8s.io/client-go/rest:go_default_library",
     ],

staging/src/k8s.io/client-go/testing/fixture.go

@@ -25,6 +25,8 @@ import (
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/runtime/schema"
+	"k8s.io/apimachinery/pkg/util/json"
+	"k8s.io/apimachinery/pkg/util/strategicpatch"
 	"k8s.io/apimachinery/pkg/watch"
 	restclient "k8s.io/client-go/rest"
 )
@@ -72,7 +74,6 @@ func ObjectReaction(tracker ObjectTracker) ReactionFunc {
 	return func(action Action) (bool, runtime.Object, error) {
 		ns := action.GetNamespace()
 		gvr := action.GetResource()
-
 		// Here and below we need to switch on implementation types,
 		// not on interfaces, as some interfaces are identical
 		// (e.g. UpdateAction and CreateAction), so if we use them,
@@ -125,6 +126,34 @@ func ObjectReaction(tracker ObjectTracker) ReactionFunc {
 			}
 			return true, nil, nil
 
+		case PatchActionImpl:
+			obj, err := tracker.Get(gvr, ns, action.GetName())
+			if err != nil {
+				// object is not registered
+				return false, nil, err
+			}
+
+			old, err := json.Marshal(obj)
+			if err != nil {
+				return true, nil, err
+			}
+			// Only supports strategic merge patch
+			// TODO: Add support for other Patch types
+			mergedByte, err := strategicpatch.StrategicMergePatch(old, action.GetPatch(), obj)
+			if err != nil {
+				return true, nil, err
+			}
+
+			if err = json.Unmarshal(mergedByte, obj); err != nil {
+				return true, nil, err
+			}
+
+			if err = tracker.Update(gvr, obj, ns); err != nil {
+				return true, nil, err
+			}
+
+			return true, obj, nil
+
 		default:
 			return false, nil, fmt.Errorf("no reaction implemented for %s", action)
 		}