通过Composer使用PHPUnit时，应在Settings | PHP | PHPUnit指向vendor/autoload.php.

You should point to your vendor/autoload.php at Settings | PHP | PHPUnit when using PHPUnit via Composer.

此博客文章包含所有详细信息(带有图片)，可以针对这种情况成功配置IDE:

This blog post has all the details (with pictures) to successfully configure IDE for such scenario: http://confluence.jetbrains.com/display/PhpStorm/PHPUnit+Installation+via+Composer+in+PhpStorm

相关的可用性标签: http://youtrack.jetbrains.com/issue/WI- 18388

PS WI-18388票证已在v8.0中修复

P.S. The WI-18388 ticket is already fixed in v8.0