How to listen to events in tests in Laravel 5?

I am trying to test emails in laravel 5 and I have realised that Swift_Mailer triggers Illuminate\Mail\Events\MessageSending event whenever a mail is being sent.

But since I am beginner, I am having trouble comprehending how to listen to this event and take out the underlying message object?

I have tried this but I don't this is correct:

public function test_the_email_via_listening_to_message_sending_event()
{
    $user = factory(User::class)->create();
    Event::fire(new UserWasCreated($user));

    Event::listen(Illuminate\Mail\Events\MessageSending::class, function($message){
        echo 'Hello';
    });
}

How to listen to a particular event in a test case and trigger code in response to it?

via Chebli Mohamed