我在Windows 10上用laragon开发项目，我已经通过composer安装了phpunit 6.2。当我运行phpunit命令在laravel项目中运行测试时发生以下错误
Warning: is_dir() expects parameter 1 to be a valid path, object given in C:\Users\ddw14\AppData\Roaming\Composer\vendor\phpunit\phpunit\src\Runner\BaseTestRunner.php on line 56
Recoverable fatal error: Object of class PHPUnit\Framework\TestSuite could not be converted to string in C:\Users\ddw14\AppData\Roaming\Composer\vendor\phpunit\phpunit\src\Runner\StandardTestSuiteLoader.php on line 32
可能是什么问题？