Laravel 7测试:尚未设置外观根

I am trying to write some tests for my my Laravel 7 app. But i keep facing the A facade root has not been set. error. And none of the other questions in SO helped me.

<?php

namespace Tests\Feature;

use Illuminate\Support\Facades\Config;
use PHPUnit\Framework\TestCase;

class AddressListenerRepositoryTest extends TestCase
{
    public function testCreate()
    {
        Config::set('x', 'address_listeners'); // Cause of "A facade root has not been set" error
    }
}

谁能解释这个错误的原因?