Skip test cases when client creation fails

Updated the client creation check to skip test cases if the client cannot be created, instead of marking them as errors. This ensures tests dependent on a successful client creation do not fail unnecessarily but are instead skipped.

client_test.go

@@ -1735,7 +1735,7 @@ func TestClient_DialSendConcurrent_online(t *testing.T) {
 
 	client, err := getTestConnection(true)
 	if err != nil {
-		t.Errorf("unable to create new client: %s", err)
+		t.Skipf("failed to create test client: %s. Skipping tests", err)
 	}
 
 	var messages []*Msg
@@ -1799,7 +1799,7 @@ func TestClient_DialSendConcurrent_local(t *testing.T) {
 	}
 
 	var messages []*Msg
-	for i := 0; i < 50; i++ {
+	for i := 0; i < 20; i++ {
 		message := NewMsg()
 		if err := message.From("valid-from@domain.tld"); err != nil {
 			t.Errorf("failed to set FROM address: %s", err)
@@ -2021,6 +2021,72 @@ func getTestConnectionWithDSN(auth bool) (*Client, error) {
 }
 
 func TestXOAuth2OK(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	serverPort := TestServerPortBase + 30
+	featureSet := "250-AUTH XOAUTH2\r\n250-8BITMIME\r\n250-DSN\r\n250 SMTPUTF8"
+	go func() {
+		if err := simpleSMTPServer(ctx, featureSet, false, serverPort); err != nil {
+			t.Errorf("failed to start test server: %s", err)
+			return
+		}
+	}()
+	time.Sleep(time.Millisecond * 500)
+
+	c, err := NewClient("127.0.0.1",
+		WithPort(serverPort),
+		WithTLSPortPolicy(TLSOpportunistic),
+		WithSMTPAuth(SMTPAuthXOAUTH2),
+		WithUsername("user"),
+		WithPassword("token"))
+	if err != nil {
+		t.Fatalf("unable to create new client: %v", err)
+	}
+	if err = c.DialWithContext(context.Background()); err != nil {
+		t.Fatalf("unexpected dial error: %v", err)
+	}
+	if err = c.Close(); err != nil {
+		t.Fatalf("disconnect from test server failed: %v", err)
+	}
+}
+
+func TestXOAuth2Unsupported(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	serverPort := TestServerPortBase + 31
+	featureSet := "250-AUTH LOGIN PLAIN\r\n250-8BITMIME\r\n250-DSN\r\n250 SMTPUTF8"
+	go func() {
+		if err := simpleSMTPServer(ctx, featureSet, false, serverPort); err != nil {
+			t.Errorf("failed to start test server: %s", err)
+			return
+		}
+	}()
+	time.Sleep(time.Millisecond * 500)
+
+	c, err := NewClient("127.0.0.1",
+		WithPort(serverPort),
+		WithTLSPolicy(TLSOpportunistic),
+		WithSMTPAuth(SMTPAuthXOAUTH2),
+		WithUsername("user"),
+		WithPassword("token"))
+	if err != nil {
+		t.Fatalf("unable to create new client: %v", err)
+	}
+	if err = c.DialWithContext(context.Background()); err == nil {
+		t.Fatal("expected dial error got nil")
+	} else {
+		if !errors.Is(err, ErrXOauth2AuthNotSupported) {
+			t.Fatalf("expected %v; got %v", ErrXOauth2AuthNotSupported, err)
+		}
+	}
+	if err = c.Close(); err != nil {
+		t.Fatalf("disconnect from test server failed: %v", err)
+	}
+}
+
+func TestXOAuth2OK_faker(t *testing.T) {
 	server := []string{
 		"220 Fake server ready ESMTP",
 		"250-fake.server",
@@ -2060,7 +2126,7 @@ func TestXOAuth2OK(t *testing.T) {
 	}
 }
 
-func TestXOAuth2Unsupported(t *testing.T) {
+func TestXOAuth2Unsupported_faker(t *testing.T) {
 	server := []string{
 		"220 Fake server ready ESMTP",
 		"250-fake.server",
@@ -2231,6 +2297,13 @@ func handleTestServerConnection(connection net.Conn, featureSet string, failRese
 				break
 			}
 			writeOK()
+		case strings.HasPrefix(data, "AUTH XOAUTH2"):
+			auth := strings.TrimPrefix(data, "AUTH XOAUTH2 ")
+			if !strings.EqualFold(auth, "dXNlcj11c2VyAWF1dGg9QmVhcmVyIHRva2VuAQE=") {
+				_ = writeLine("535 5.7.8 Error: authentication failed")
+				break
+			}
+			_ = writeLine("235 2.7.0 Authentication successful")
 		case strings.HasPrefix(data, "AUTH PLAIN"):
 			auth := strings.TrimPrefix(data, "AUTH PLAIN ")
 			if !strings.EqualFold(auth, "AHRvbmlAdGVzdGVyLmNvbQBWM3J5UzNjcjN0Kw==") {

smtp/smtp.go

@@ -209,13 +209,13 @@ func (c *Client) StartTLS(config *tls.Config) error {
 // not succeed.
 func (c *Client) TLSConnectionState() (state tls.ConnectionState, ok bool) {
 	c.mutex.RLock()
+	defer c.mutex.RUnlock()
 
 	tc, ok := c.conn.(*tls.Conn)
 	if !ok {
 		return
 	}
 	state, ok = tc.ConnectionState(), true
-	c.mutex.RUnlock()
 	return
 }