通过composer安装PHPUnit的工作正常.事实证明，我的作曲家安装在某种程度上出错了.成功安装composer之后，我让它处理PHPUnit的安装.在那之后，它就起作用了.测试在IDE中工作正常，服务器再次响应.谢谢LazyOne.

Installation of PHPUnit via composer worked. It turns out my composer installation went wrong in some way. After composer was successfully installed, I let it handle installing PHPUnit. After that it just worked. Tests work fine in the IDE and the server is responsive again. Thanks LazyOne.