class FooTest extends WebTestCase
{
    public function testGetContainerA()
    {
        $kernel = self::bootKernel();
        $container = $kernel->getContainer();
    }

    public function testGetContainerB()
    {
        self::bootKernel();
        $container = self::$container;
    }

    public function testGetContainerC()
    {
        $client = self::createClient();
        $container = $client->getContainer();
    }
}

class FooTest extends WebTestCase
{
    public function testGetContainerTheOnlyWayYouShouldUse()
    {
        $container = $this->getContainer();
    }
}