Symfony and PhpUnit memory leak

We have issues with memory leak when loading Doctrine in our phpunit tests

Starting for Symfony's documentation : http://symfony.com/doc/2.7/cookbook/testing/doctrine.html we have written this test :

use Symfony\Bundle\FrameworkBundle\Test\KernelTestCase;

class memoryleakTest extends KernelTestCase
{
    private $em;

    protected function setUp()
    {
        self::bootKernel();

        $this->em = static::$kernel->getContainer()
            ->get('doctrine')
            ->getManager();
    }

    protected function tearDown()
    {
        parent::tearDown();

        $this->em->close();
    }

    function testEEE1()  { 
    }
    function testEEE2()  { 
    }
    function testEEE3()  { 
    }
    function testEEE4()  { 
    }
    function testEEE5()  { 
    }
    function testEEE6()  { 
    }
    function testEEE7()  { 
    }
    function testEEE8()  { 
    }
    function testEEE9()  { 
    }
    function testEEE10()  { 
    }
    function testEEE11()  { 
    }
    function testEEE12()  { 
    }
    function testEEE13()  { 
    }
    function testEEE14()  { 
    }
    function testEEE15()  { 
    }
    function testEEE16()  { 
    }
}

we got this result (php_memory_usage between parenthesis) :

testEEE1: . (42M)
testEEE2: . (42.7M)
testEEE3: . (43.3M)
testEEE4: . (44M)
testEEE5: . (44.8M)
testEEE6: . (45.5M)
testEEE7: . (46.1M)
testEEE8: . (46.8M)
testEEE9: . (47.4M)
testEEE10: . (48.1M)
testEEE11: . (48.7M)
testEEE12: . (49.4M)
testEEE13: . (50.1M)
testEEE14: . (50.7M)
testEEE15: . (51.4M)
testEEE16: . (52M)

If we remove the doctrine manager loading in setup, we got (32,7M) for each test

Is it a proper way to unload doctrine after each test in the teardown function ?