ManyToManyTest.php

<?php 
class ManyToManyTest extends \PHPUnit_Framework_TestCase

{
    public function testSynchronization()
    {
        $post = new Post();
        $tag = new Tag();
        
        $post->addTag($tag);

        // $tag not contains the $post
        $this->assertFalse($tag->getPosts()->contains($post));
        
        $tag->addPost($post);
        
        // now $tag contains the $post
        $this->assertTrue($tag->getPosts()->contains($post));
    }
    

}