test event listener

TestListener.php

<?php

public function test_was_called()
{
    $eventDispatcher = new EventDispatcher();
    $mockLlistener = $this->createMock(Listener::class);
    $mockListener
        ->expects($this->once())
        ->method('onData');

    $eventDispatcher->addListener('acme.foo.bar', [$listener, 'onData']);

    $mockEvent = $this->createMock(Event::class); // Event has dependencies 
    $eventDispatcher->dispatch('acme.foo.bar', $mockEvent);
}