Assert that the pluggable mail system is functional.
public function testPluggableFramework() {
$language_interface = language(Language::TYPE_INTERFACE);
// Use MailTestCase for sending a message.
$message = drupal_mail('simpletest', 'mail_test', 'testing@example.com', $language_interface->langcode);
// Assert whether the message was sent through the send function.
$this
->assertEqual(self::$sent_message['to'], 'testing@example.com', 'Pluggable mail system is extendable.');
}