访问配置值

I am trying to access to config values, in order to pass a token to a constructor and be able to add it to the headers. So basically what I did was in the TestCase class, in the constructor

use Illuminate\Support\Facades\Config;

public function __construct()
{
    parent::__construct();

   $this->token = Config::get('app.token');

}

Here I am getting:

PHP Fatal error: Uncaught RuntimeException: A facade root has not been set

Also, I tried with:

$this->token = config('app.token');

And here

PHP Fatal error: Uncaught ReflectionException: Class config does not exist.

My other question would be, in case I can get the token, how do I can pass it to the header.

Thank you, and I hope you can understand what I tried to explain.

Use app container of the TestCase class;

The application container is available after setUp lifecycle method of the TestCase and not during it's construction.

function setUp(): void 
{
    parent::setUp();

    $config = $this->app['config'];
    $this->token = $config->get('app.token');
}