brought etcdv3 registrar only test to its own run

sd/etcdv3/integration_test.go

@@ -36,14 +36,6 @@ func runIntegration(settings integrationSettings, client Client, service Service
 	registrar.Register()
 	t.Log("Registered")
 
-	// Deregister our instance. (so we test registrar only scenario)
-	registrar.Deregister()
-	t.Log("Deregistered")
-
-	// Re-Register our instance.
-	registrar.Register()
-	t.Log("Registered")
-
 	// Retrieve entries from etcd manually.
 	entries, err = client.GetEntries(settings.key)
 	if err != nil {
@@ -172,6 +164,50 @@ func TestIntegrationTTL(t *testing.T) {
 	runIntegration(settings, client, service, t)
 }
 
+func TestIntegrationRegistrarOnly(t *testing.T) {
+	settings := testIntegrationSettings(t)
+	client, err := NewClient(context.Background(), []string{settings.addr}, ClientOptions{
+		DialTimeout:   2 * time.Second,
+		DialKeepAlive: 2 * time.Second,
+	})
+	if err != nil {
+		t.Fatalf("NewClient(%q): %v", settings.addr, err)
+	}
+
+	service := Service{
+		Key:   settings.key,
+		Value: settings.value,
+		TTL:   NewTTLOption(time.Second*3, time.Second*10),
+	}
+	defer client.Deregister(service)
+
+	// Verify test data is initially empty.
+	entries, err := client.GetEntries(settings.key)
+	if err != nil {
+		t.Fatalf("GetEntries(%q): expected no error, got one: %v", settings.key, err)
+	}
+	if len(entries) > 0 {
+		t.Fatalf("GetEntries(%q): expected no instance entries, got %d", settings.key, len(entries))
+	}
+	t.Logf("GetEntries(%q): %v (OK)", settings.key, entries)
+
+	// Instantiate a new Registrar, passing in test data.
+	registrar := NewRegistrar(
+		client,
+		service,
+		log.With(log.NewLogfmtLogger(os.Stderr), "component", "registrar"),
+	)
+
+	// Register our instance.
+	registrar.Register()
+	t.Log("Registered")
+
+	// Deregister our instance. (so we test registrar only scenario)
+	registrar.Deregister()
+	t.Log("Deregistered")
+
+}
+
 func within(d time.Duration, f func() bool) bool {
 	deadline := time.Now().Add(d)
 	for time.Now().Before(deadline) {