Fatal error: Uncaught Error: Class "PHPUnit\Framework\TestCase" not found in C:\xampp\htdocs\Backend_v.004\vendor\marcj\topsort\tests\Tests\SimpleSortTest.php:21 Stack trace: #0 {main} thrown in C:\xampp\htdocs\Backend_v.004\vendor\marcj\topsort\tests\Tests\SimpleSortTest.php on line 21