Fatal error: Uncaught Error: Class "PHPUnit\Framework\TestCase" not found in C:\xampp\htdocs\r10csm\vendor\guzzlehttp\promises\tests\PromiseTest.php:18 Stack trace: #0 {main} thrown in C:\xampp\htdocs\r10csm\vendor\guzzlehttp\promises\tests\PromiseTest.php on line 18