Laravel unit testing calling a Route from a Test with authentication

I'm testing my api. Before calling a route I log in user to application. Problem is that after authentication user's id is not assigned to Auth::id() within route call.

Here is the scenario:

Test method:

public function testApiGetOrder()
{
    var_dump($this->user);  // first dump
    Auth::login($this->user); // Can't use $this->be($this->user) here, it would not help anyway...
    var_dump(Auth::id());  // second dump

    $response = $this->call('GET', '/order/' . $this->order->getKey());

    $this->assertResponseOk();
    $this->assertJson($response->getContent());
    $this->assertJsonStringEqualsJsonString($this->order->toJson(), $response->getContent());
}

OrderController's method:

public function show($id)
{
    var_dump(Auth::id());  // third dump
    var_dump(Auth::user()->getKey());   // fourth dump

    // Calling model's logic here
}

Output of of testApiGetOrder:

First dump: object(User)

Second dump: int(1)

Third dump: NULL

Fourth dump: int(1)

Why the value of user's id is not assigned to Auth::id() ?