BadMethodCallException: Method Mockery_0_Illuminate_Contracts_Events_Dispatcher::listen() does not exist on this mock object

I'm doing some unit testing and want to test so basic stuff. In my test I'mg using Illuminate\Foundation\Testing\WithoutEvents.

When an user registers he or she get's an activation mail. First I used an Observer for that, but came to the conclusion that Laravel doesn't disable the observers when using WithoutEvents as writen here and here. Then I changed my code to the 'traditional' event and listeners.

EventServiceProvider is still default, except for the $listen property:

/**
 * The event listener mappings for the application.
 *
 * @var array
 */
protected $listen = [
    'App\Events\UserCreated' => [
        'App\Listeners\CreateActivation'
    ],
];

When I dispatch the event:

event(new UserCreated($user));

And an example test (which fails):

class ExampleTest extends TestCase
{
    use DatabaseMigrations, WithoutEvents;

    public function testExample()
    {
        $user = factory(User::class)->create();
    }
}

The error:

I've no clue why it's is crashing. Any help is much appreciated. Also, if I need to provide more code let me know. Because I'm not sure where the problem is caused.

via Chebli Mohamed