This is an example of integrating MuffinFactory 3.0 into a Symfony 2 functional test

ExampleControllerTestCase.php

<?php
namespace Acme\DemoBundle\Tests\Controller;

use Symfony\Bundle\FrameworkBundle\Test\WebTestCase;
use League\FactoryMuffin\FactoryMuffin;
use League\FactoryMuffin\Stores\RepositoryStore;

class ExampleControllerTest extends WebTestCase
{
    /**
     * @var FactoryMuffin
     */
    protected static $fm;

    /**
     * The static setup method before the tests are executed
     * Great for setting up the model factories
     *
     */
    public static function setupBeforeClass()
    {
        $client = static::createClient();
        $container = $client->getContainer();
        $em = $container->get('doctrine.orm.entity_manager');

        // overriding the default "store" which is an eloquent interpretation with a repository one
        $store = new RepositoryStore($em);

        // create a new factory muffin instance
        static::$fm = new FactoryMuffin($store);

        // load your model definitions
        static::$fm->loadFactories(__DIR__.'/../factories');
    }
  
    /**
     * The actual test
     */
    public function testIndexAction()
    {
        $client = static::createClient();
        $something = static::$fm->create('Acme\DemoBundle\Entity\Something');
        $this->assertInstanceOf('Acme\DemoBundle\Entity\Something', $something);
    }
  
    /**
     * Deleting the persisted models after the test is over
     */
    public static function tearDownAfterClass()
    {
        static::$fm->deleteSaved();
    }
}

Does your Acme\DemoBundle\Entity\Something have setters?