vtworkerclient: Add UnregisterFactoryForTest().

This way, different fakes can be used in the same package. This was already done for vtctlclient.

go/vt/automation/split_clone_task_test.go

@@ -15,6 +15,7 @@ import (
 func TestSplitCloneTask(t *testing.T) {
 	fake := fakevtworkerclient.NewFakeVtworkerClient()
 	vtworkerclient.RegisterFactory("fake", fake.FakeVtworkerClientFactory)
+	defer vtworkerclient.UnregisterFactoryForTest("fake")
 	flag.Set("vtworker_client_protocol", "fake")
 	fake.RegisterResult([]string{"SplitClone", "--strategy=-populate_blp_checkpoint", "test_keyspace/0"},
 		"",  // No output.

go/vt/worker/vtworkerclient/interface.go

@@ -46,6 +46,17 @@ func RegisterFactory(name string, factory Factory) {
 	factories[name] = factory
 }
 
+// UnregisterFactoryForTest allows to unregister a client implementation from the static map.
+// This function is used by unit tests to cleanly unregister any fake implementations.
+// This way, a test package can use the same name for different fakes and no dangling fakes are
+// left behind in the static factories map after the test.
+func UnregisterFactoryForTest(name string) {
+	if _, ok := factories[name]; !ok {
+		log.Fatalf("UnregisterFactoryForTest: %s is not registered", name)
+	}
+	delete(factories, name)
+}
+
 // New allows a user of the client library to get its implementation.
 func New(addr string, connectTimeout time.Duration) (Client, error) {
 	factory, ok := factories[*protocol]