Add client-go example using fake client in test.

This adds an example showing the steps needed to get a working
SharedInformerFactory with a fake client for testing.

staging/BUILD

@@ -104,6 +104,7 @@ filegroup(
         "//staging/src/k8s.io/client-go/discovery:all-srcs",
         "//staging/src/k8s.io/client-go/dynamic:all-srcs",
         "//staging/src/k8s.io/client-go/examples/create-update-delete-deployment:all-srcs",
+        "//staging/src/k8s.io/client-go/examples/fake-client:all-srcs",
         "//staging/src/k8s.io/client-go/examples/in-cluster-client-configuration:all-srcs",
         "//staging/src/k8s.io/client-go/examples/out-of-cluster-client-configuration:all-srcs",
         "//staging/src/k8s.io/client-go/examples/workqueue:all-srcs",

staging/src/k8s.io/client-go/examples/README.md

@@ -25,3 +25,7 @@ for client-go.
   the custom resources.
 
 [informer]: https://godoc.org/k8s.io/client-go/tools/cache#NewInformer
+
+### Testing
+
+- [**Fake Client**](./fake-client): Use a fake client in tests.

staging/src/k8s.io/client-go/examples/fake-client/BUILD

@@ -0,0 +1,27 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_test")
+
+go_test(
+    name = "go_default_test",
+    srcs = ["main_test.go"],
+    deps = [
+        "//vendor/k8s.io/api/core/v1:go_default_library",
+        "//vendor/k8s.io/apimachinery/pkg/apis/meta/v1:go_default_library",
+        "//vendor/k8s.io/client-go/informers:go_default_library",
+        "//vendor/k8s.io/client-go/kubernetes/fake:go_default_library",
+        "//vendor/k8s.io/client-go/tools/cache:go_default_library",
+    ],
+)
+
+filegroup(
+    name = "package-srcs",
+    srcs = glob(["**"]),
+    tags = ["automanaged"],
+    visibility = ["//visibility:private"],
+)
+
+filegroup(
+    name = "all-srcs",
+    srcs = [":package-srcs"],
+    tags = ["automanaged"],
+    visibility = ["//visibility:public"],
+)

staging/src/k8s.io/client-go/examples/fake-client/README.md

@@ -0,0 +1,14 @@
+# Fake Client Example
+
+This example demonstrates how to use a fake client with SharedInformerFactory in tests.
+
+It covers:
+ * Creating the fake client
+ * Setting up real informers
+ * Injecting events into those informers
+
+## Running
+
+```
+go test -v k8s.io/client-go/examples/fake-client
+```

staging/src/k8s.io/client-go/examples/fake-client/main_test.go

@@ -0,0 +1,77 @@
+/*
+Copyright 2018 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package fakeclient
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"k8s.io/api/core/v1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/client-go/informers"
+	"k8s.io/client-go/kubernetes/fake"
+	"k8s.io/client-go/tools/cache"
+)
+
+// TestFakeClient demonstrates how to use a fake client with SharedInformerFactory in tests.
+func TestFakeClient(t *testing.T) {
+	// Use a timeout to keep the test from hanging.
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+
+	// Create the fake client.
+	client := fake.NewSimpleClientset()
+
+	// We will create an informer that writes added pods to a channel.
+	pods := make(chan *v1.Pod, 1)
+	informers := informers.NewSharedInformerFactory(client, 0)
+	podInformer := informers.Core().V1().Pods().Informer()
+	podInformer.AddEventHandler(&cache.ResourceEventHandlerFuncs{
+		AddFunc: func(obj interface{}) {
+			pod := obj.(*v1.Pod)
+			t.Logf("pod added: %s/%s", pod.Namespace, pod.Name)
+			pods <- pod
+			cancel()
+		},
+	})
+
+	// Make sure informers are running.
+	informers.Start(ctx.Done())
+
+	// This is not required in tests, but it serves as a proof-of-concept by
+	// ensuring that the informer goroutine have warmed up and called List before
+	// we send any events to it.
+	for !podInformer.HasSynced() {
+		time.Sleep(10 * time.Millisecond)
+	}
+
+	// Inject an event into the fake client.
+	p := &v1.Pod{ObjectMeta: metav1.ObjectMeta{Name: "my-pod"}}
+	_, err := client.Core().Pods("test-ns").Create(p)
+	if err != nil {
+		t.Errorf("error injecting pod add: %v", err)
+	}
+
+	// Wait and check result.
+	<-ctx.Done()
+	select {
+	case pod := <-pods:
+		t.Logf("Got pod from channel: %s/%s", pod.Namespace, pod.Name)
+	default:
+		t.Error("Informer did not get the added pod")
+	}
+}