title: find external test file for unit test by relative path c++ cmake guest
body: <p>What would be the proper way to access an external test file for the unit test of a c++ project? I am using CMake and Gtest.</p>
  
  <p>This is a sample of the directory structure.</p>
  
  <pre><code>Project
     -src
         -test (unit tests here)
     -test-data (data file here)
  </code></pre>
  
  <p>Thanks!</p>