title: What does enable_testing() do in cmake?
body: <p>I see that to add my google tests(for my cpp project), I need to make a call to enable_testing() in the root source directory. Can someone explain what this really does? Also why would cmake not make this default?</p>
  
  <p>This is all I could get from the documentation.</p>
  
  <blockquote>
    <p>Enables testing for this directory and below. See also the add_test()
    command. Note that ctest expects to find a test file in the build
    directory root. Therefore, this command should be in the source
    directory root.</p>
  </blockquote>