title: qmake checking for library
body: <p>I have a qt project setup as a subdirs project with my source code in a src directory and unit testing code setup in a test directory.  Each has its own project file.  I want to be able to compile the source on other computers, but they may not have the googletest library setup.  I have looked at the qmake test function "requires()" and "packagesExist()" however, they do not seem to be built to handle external libraries.</p>
  
  <p>How can I instruct qmake to skip the test project if the testing library is not found?</p>