Fix go buildable source file problem (#1213)

examples/helloworld/mock_helloworld/hw_mock_test.go

@@ -0,0 +1,49 @@
+package mock_helloworld_test
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/golang/mock/gomock"
+	"github.com/golang/protobuf/proto"
+	"golang.org/x/net/context"
+	helloworld "google.golang.org/grpc/examples/helloworld/helloworld"
+	hwmock "google.golang.org/grpc/examples/helloworld/mock_helloworld"
+)
+
+// rpcMsg implements the gomock.Matcher interface
+type rpcMsg struct {
+	msg proto.Message
+}
+
+func (r *rpcMsg) Matches(msg interface{}) bool {
+	m, ok := msg.(proto.Message)
+	if !ok {
+		return false
+	}
+	return proto.Equal(m, r.msg)
+}
+
+func (r *rpcMsg) String() string {
+	return fmt.Sprintf("is %s", r.msg)
+}
+
+func TestSayHello(t *testing.T) {
+	ctrl := gomock.NewController(t)
+	defer ctrl.Finish()
+	mockGreeterClient := hwmock.NewMockGreeterClient(ctrl)
+	req := &helloworld.HelloRequest{Name: "unit_test"}
+	mockGreeterClient.EXPECT().SayHello(
+		gomock.Any(),
+		&rpcMsg{msg: req},
+	).Return(&helloworld.HelloReply{Message: "Mocked Interface"}, nil)
+	testSayHello(t, mockGreeterClient)
+}
+
+func testSayHello(t *testing.T, client helloworld.GreeterClient) {
+	r, err := client.SayHello(context.Background(), &helloworld.HelloRequest{Name: "unit_test"})
+	if err != nil || r.Message != "Mocked Interface" {
+		t.Errorf("mocking failed")
+	}
+	t.Log("Reply : ", r.Message)
+}