EventListener.php

<?php
/**
 * Symphony CMS
 */
namespace SymphonyCMS;

/**
 * Event Listener
 */
class EventListener implements ListenerInterface
{
    /**
     * The event to listen for
     * @var string
     */
    protected $event;

    /**
     * The callback to run at transaction time
     * @var Closure
     */
    protected $callback;

    /**
     * Sets the event to listen for, or retrieves the event being listened to
     * @param  string $event
     * @return string
     */
    public function event($event = null)
    {
        if (is_null($event)) {
            return $this->event;
        }

        $this->event = $event;
    }

    /**
     * Sets the callback
     * @param  Closure  $callback
     */
    public function callback(\Closure $callback)
    {
        $this->callback = $callback;
    }

    /**
     * Run the callback on the transaction data
     * @param  array $data
     */
    public function execute(&$data)
    {
        $callback = $this->callback;

        $data = $callback($data);
        // var_dump($data);die;
    }
}

EventListenerTest.php

<?php
/**
 * Symphony CMS Tests
 */
namespace SymphonyCMS\Tests;

use \SymphonyCMS\EventListener;
use \SymphonyCMS\Transaction;

/**
 * Listener Stack Test
 */
class EventListenerTest extends \PHPUnit_Framework_TestCase
{
    public function setUp()
    {
        $this->listener = new EventListener;
        $this->event = 'my-test-event';
    }

    public function getInternal($source)
    {
        $reflection = new \ReflectionClass($this->listener);
        $property = $reflection->getProperty($source);
        $property->setAccessible(true);

        return $property->getValue($this->listener);
    }

    public function testSetEvent()
    {
        $this->listener->event($this->event);

        $event = $this->getInternal('event');

        $this->assertEquals($this->event, $event);
    }

    public function testGetEvent()
    {
        $reflection = new \ReflectionClass($this->listener);
        $property = $reflection->getProperty('event');
        $property->setAccessible(true);
        $property->setValue($this->listener, $this->event);

        $this->assertEquals($this->event, $this->listener->event());
    }

    public function testCallback()
    {
        $this->listener->callback(function () {
            return 'callback returns value';
        });

        $callback = $this->getInternal('callback');

        $this->assertInstanceOf('Closure', $callback);
        $this->assertEquals('callback returns value', $callback());
    }

    public function testExecute()
    {
        $data = [
            'key' => false
        ];

        $this->listener->callback(function ($data) {
            $data['key'] = true;
            return $data;
        });

        $this->listener->execute($data);

        var_dump($data);die;
    }
}