Problems with middleware (auth:api) on non-GET requests

Hey guys, I'm giving a try to the new api stuff on laravel 5.3. It works great on the app itself or in apps like insomnia or postman; but is making me crazy on the tests.

Basically, app goes nuts on any non-GET requests.

For example, this test passes:

/** @test */
    public function index_should_retrieve_list_of_users_categories()
    {
        $data = ['api_token' => $this->user->api_token];

        $response = $this->call('GET', route('categories.index'), $data);

        $this->seeStatusCode(200);
        $this->assertJson($response->getContent());
        $this->seeJsonStructure([
            '*' => ['id', 'user_id', 'name', 'color'],
        ]);

        $data = json_decode($response->getContent(), true);

        // check all items returned belong to user
        foreach ($data as $item) {
            $this->assertTrue($item['user_id'] == $this->user->id);
        }
    }

But when trying this other:

/** @test */
    public function store_should_store_a_new_category()
    {
        $data = [
            'api_token' => $this->user->api_token,
            'name' => 'test category',
            'color' => '#123456'
        ];

        $response = $this->call('POST', route('categories.store'), $data);


        $this->seeStatusCode(200);
        $this->assertJson($response->getContent());
        $this->seeJsonStructure([
            'user_id',
            'name',
            'color'
        ]);

        $answer = json_decode($response->getContent(), true);

        $this->assertTrue($answer['user_id'] == $this->user->id);
        $this->assertTrue($answer['name'] == $data['name']);
        $this->assertTrue($answer['color'] == $data['color']);
    }

It fails receiving a 302 redirect to /login.

If I'm sending api_token for both requests, how can I be properly authenticated for the first one but not for the second?

Again, it works on any manual test I've tried (cURL requests on teh console, browser, insomnia, postman, etc.); it only fails on phpUnit. I don't understand why.