diff --git a/Tests/Transport/MailgunApiTransportTest.php b/Tests/Transport/MailgunApiTransportTest.php
index f30fa02..b4d2356 100644
--- a/Tests/Transport/MailgunApiTransportTest.php
+++ b/Tests/Transport/MailgunApiTransportTest.php
@@ -12,10 +12,14 @@
 namespace Symfony\Component\Mailer\Bridge\Mailgun\Tests\Transport;
 
 use PHPUnit\Framework\TestCase;
+use Symfony\Component\HttpClient\MockHttpClient;
+use Symfony\Component\HttpClient\Response\MockResponse;
 use Symfony\Component\Mailer\Bridge\Mailgun\Transport\MailgunApiTransport;
 use Symfony\Component\Mailer\Envelope;
+use Symfony\Component\Mailer\Exception\HttpTransportException;
 use Symfony\Component\Mime\Address;
 use Symfony\Component\Mime\Email;
+use Symfony\Contracts\HttpClient\ResponseInterface;
 
 class MailgunApiTransportTest extends TestCase
 {
@@ -64,4 +68,67 @@ public function testCustomHeader()
         $this->assertArrayHasKey('h:x-mailgun-variables', $payload);
         $this->assertEquals($json, $payload['h:x-mailgun-variables']);
     }
+
+    public function testSend()
+    {
+        $client = new MockHttpClient(function (string $method, string $url, array $options): ResponseInterface {
+            $this->assertSame('POST', $method);
+            $this->assertSame('https://api.us-east-1.mailgun.net:8984/v3/symfony/messages', $url);
+            $this->assertStringContainsString('Basic YXBpOkFDQ0VTU19LRVk=', $options['headers'][2] ?? $options['request_headers'][1]);
+
+            $content = '';
+            while ($chunk = $options['body']()) {
+                $content .= $chunk;
+            }
+
+            $this->assertStringContainsString('Hello!', $content);
+            $this->assertStringContainsString('Saif Eddin <saif.gmati@symfony.com>', $content);
+            $this->assertStringContainsString('Fabien <fabpot@symfony.com>', $content);
+            $this->assertStringContainsString('Hello There!', $content);
+
+            return new MockResponse(json_encode(['id' => 'foobar']), [
+                'http_code' => 200,
+            ]);
+        });
+        $transport = new MailgunApiTransport('ACCESS_KEY', 'symfony', 'us-east-1', $client);
+        $transport->setPort(8984);
+
+        $mail = new Email();
+        $mail->subject('Hello!')
+            ->to(new Address('saif.gmati@symfony.com', 'Saif Eddin'))
+            ->from(new Address('fabpot@symfony.com', 'Fabien'))
+            ->text('Hello There!');
+
+        $message = $transport->send($mail);
+
+        $this->assertSame('foobar', $message->getMessageId());
+    }
+
+    public function testSendThrowsForErrorResponse()
+    {
+        $client = new MockHttpClient(function (string $method, string $url, array $options): ResponseInterface {
+            $this->assertSame('POST', $method);
+            $this->assertSame('https://api.mailgun.net:8984/v3/symfony/messages', $url);
+            $this->assertStringContainsStringIgnoringCase('Authorization: Basic YXBpOkFDQ0VTU19LRVk=', $options['headers'][2] ?? $options['request_headers'][1]);
+
+            return new MockResponse(json_encode(['message' => 'i\'m a teapot']), [
+                'http_code' => 418,
+                'response_headers' => [
+                    'content-type' => 'application/json',
+                ],
+            ]);
+        });
+        $transport = new MailgunApiTransport('ACCESS_KEY', 'symfony', 'us', $client);
+        $transport->setPort(8984);
+
+        $mail = new Email();
+        $mail->subject('Hello!')
+            ->to(new Address('saif.gmati@symfony.com', 'Saif Eddin'))
+            ->from(new Address('fabpot@symfony.com', 'Fabien'))
+            ->text('Hello There!');
+
+        $this->expectException(HttpTransportException::class);
+        $this->expectExceptionMessage('Unable to send an email: i\'m a teapot (code 418).');
+        $transport->send($mail);
+    }
 }
diff --git a/Tests/Transport/MailgunHttpTransportTest.php b/Tests/Transport/MailgunHttpTransportTest.php
index 9b57b2b..a50f1ff 100644
--- a/Tests/Transport/MailgunHttpTransportTest.php
+++ b/Tests/Transport/MailgunHttpTransportTest.php
@@ -12,7 +12,13 @@
 namespace Symfony\Component\Mailer\Bridge\Mailgun\Tests\Transport;
 
 use PHPUnit\Framework\TestCase;
+use Symfony\Component\HttpClient\MockHttpClient;
+use Symfony\Component\HttpClient\Response\MockResponse;
 use Symfony\Component\Mailer\Bridge\Mailgun\Transport\MailgunHttpTransport;
+use Symfony\Component\Mailer\Exception\HttpTransportException;
+use Symfony\Component\Mime\Address;
+use Symfony\Component\Mime\Email;
+use Symfony\Contracts\HttpClient\ResponseInterface;
 
 class MailgunHttpTransportTest extends TestCase
 {
@@ -45,4 +51,67 @@ public function getTransportData()
             ],
         ];
     }
+
+    public function testSend()
+    {
+        $client = new MockHttpClient(function (string $method, string $url, array $options): ResponseInterface {
+            $this->assertSame('POST', $method);
+            $this->assertSame('https://api.us-east-1.mailgun.net:8984/v3/symfony/messages.mime', $url);
+            $this->assertStringContainsString('Basic YXBpOkFDQ0VTU19LRVk=', $options['headers'][2] ?? $options['request_headers'][1]);
+
+            $content = '';
+            while ($chunk = $options['body']()) {
+                $content .= $chunk;
+            }
+
+            $this->assertStringContainsString('Subject: Hello!', $content);
+            $this->assertStringContainsString('To: Saif Eddin <saif.gmati@symfony.com>', $content);
+            $this->assertStringContainsString('From: Fabien <fabpot@symfony.com>', $content);
+            $this->assertStringContainsString('Hello There!', $content);
+
+            return new MockResponse(json_encode(['id' => 'foobar']), [
+                'http_code' => 200,
+            ]);
+        });
+        $transport = new MailgunHttpTransport('ACCESS_KEY', 'symfony', 'us-east-1', $client);
+        $transport->setPort(8984);
+
+        $mail = new Email();
+        $mail->subject('Hello!')
+            ->to(new Address('saif.gmati@symfony.com', 'Saif Eddin'))
+            ->from(new Address('fabpot@symfony.com', 'Fabien'))
+            ->text('Hello There!');
+
+        $message = $transport->send($mail);
+
+        $this->assertSame('foobar', $message->getMessageId());
+    }
+
+    public function testSendThrowsForErrorResponse()
+    {
+        $client = new MockHttpClient(function (string $method, string $url, array $options): ResponseInterface {
+            $this->assertSame('POST', $method);
+            $this->assertSame('https://api.mailgun.net:8984/v3/symfony/messages.mime', $url);
+            $this->assertStringContainsString('Basic YXBpOkFDQ0VTU19LRVk=', $options['headers'][2] ?? $options['request_headers'][1]);
+
+            return new MockResponse(json_encode(['message' => 'i\'m a teapot']), [
+                'http_code' => 418,
+                'response_headers' => [
+                    'content-type' => 'application/json',
+                ],
+            ]);
+        });
+        $transport = new MailgunHttpTransport('ACCESS_KEY', 'symfony', 'us', $client);
+        $transport->setPort(8984);
+
+        $mail = new Email();
+        $mail->subject('Hello!')
+            ->to(new Address('saif.gmati@symfony.com', 'Saif Eddin'))
+            ->from(new Address('fabpot@symfony.com', 'Fabien'))
+            ->text('Hello There!');
+
+        $this->expectException(HttpTransportException::class);
+        $this->expectExceptionMessage('Unable to send an email: i\'m a teapot (code 418).');
+        $transport->send($mail);
+    }
 }