What difference between symfony's testing and browser

I encounter a problem with symfony's testing.
Here is my action source code:

public function indexAction()
{
    $yac = new \Yac();
    return new JsonResponse($yac->info());
}

And this is my testing source code:

public function testIndex()
{
    $client = static::createClient();
    $client->request('GET', 'http://admin.yjj.com/');
}

Position A get false, when using phpunit to test. The screenshot is below:

But it's normal when using browser. The result:

{
    "memory_size": 71303168, 
    "slots_memory_size": 4194304, 
    "values_memory_size": 67108864, 
    "segment_size": 4194304, 
    "segment_num": 16, 
    "miss": 0, 
    "hits": 0, 
    "fails": 0, 
    "kicks": 0, 
    "recycles": 0, 
    "slots_size": 32768, 
    "slots_used": 0
}

So, I don't know what difference between symfony's testing and browser.
Or, this is the problem of Yac extension?