Fatal error: Uncaught Error: Class "PHPUnit\Framework\TestCase" not found in C:\xampp\htdocs\smsgateway\tests\Unit\Infrastructure\Smpp\SerializedSubmitSmPduTest.php:16 Stack trace: #0 {main} thrown in C:\xampp\htdocs\smsgateway\tests\Unit\Infrastructure\Smpp\SerializedSubmitSmPduTest.php on line 16