testing memory size

As per Jeffrey's forum workflow, I am building some tests to run on my Laravel API, and following his steps, i'm using the :memory: sqlite feature in phpunit.

On the very first test that is failing, I thought I would var_dump the $response, so that I can see what is happening, and on the var_dump line itself, i'm getting the error:

  [Symfony\Component\Debug\Exception\FatalErrorException]
   Allowed memory size of 134217728 bytes exhausted (tried to allocate 119554048 bytes)

Its a simple POST request with body something like this

          $response = $this->withHeaders([
        'Accept' => 'application/json',
        'Content_Type' => 'application_json'
    ])->json('POST', '/cart', $cart);

$cart is simply an array for the body of the request.

Is this a limitation of doing POST requests with the sqlite :memory: ?