Unit Tests Unable To Find Class

I have a test case called ApiUserServicesTest in protected/tests/unit/modules/api and the class it’s testing is in protected/modules/api/modules/v1_0/implementations/ApiUserServices.php. When I run the test, PHPUnit throws the error “include(ApiUserServices.php): failed to open stream: No such file or directory”.

Is there any reason that my class wouldn’t be visible to my test case?