404 on simple test example?

Hi there, I am trying to get the example of tests running on my 5.1 installation:

<<?php

use Illuminate\Foundation\Testing\WithoutMiddleware;
use Illuminate\Foundation\Testing\DatabaseMigrations;
use Illuminate\Foundation\Testing\DatabaseTransactions;

class ExampleTest extends TestCase
{
    /**
     * A basic functional test example.
     *
     * @return void
     */
    protected $baseUrl = 'https://localhost/abschlussprojekt/public/';
    
    public function testBasicExample()
    {
        $this->visit('/')
             ->see('Testeintrag');
    }
}

But I always get :

1. ExampleTest::testBasicExample A request to [URL] failed. Received status code [404].

I know the url is right, because copying it from the command line to the browser works. Any ideas on this one?