[5.3] Added support for notifications MailChannel using messages that implements Mailable contract

tests/Notifications/NotificationMailChannelTest.php

@@ -210,6 +210,20 @@ public function testMessageWithToAddress()
 
         $channel->send($notifiable, $notification);
     }
+
+    public function testMessageWithMailableContract()
+    {
+        $notification = new NotificationMailChannelTestNotificationWithMailableContract;
+        $notifiable = new NotificationMailChannelTestNotifiable;
+
+        $channel = new Illuminate\Notifications\Channels\MailChannel(
+            $mailer = Mockery::mock(Illuminate\Contracts\Mail\Mailer::class)
+        );
+
+        $mailer->shouldReceive('send')->once();
+
+        $channel->send($notifiable, $notification);
+    }
 }
 
 class NotificationMailChannelTestNotifiable
@@ -272,3 +286,23 @@ public function toMail($notifiable)
             ->to('jeffrey@laracasts.com');
     }
 }
+
+class NotificationMailChannelTestNotificationWithMailableContract extends Notification
+{
+    public function toMail($notifiable)
+    {
+        $mock = Mockery::mock(Illuminate\Contracts\Mail\Mailable::class);
+
+        $mock->shouldReceive('send')->once()->with(Mockery::on(function($mailer) {
+            if (! ($mailer instanceof \Illuminate\Contracts\Mail\Mailer)) {
+                return false;
+            }
+
+            $mailer->send('notifications::email-plain');
+
+            return true;
+        }));
+
+        return $mock;
+    }
+}