title: CMakelist - if(DEFINED) syntax
body: <p>I was going through a CMakelist.txt file which has an entry for a C++ project containing a <strong>src</strong> and a <strong>tests</strong> folder.
  I need to know what does the following syntax means?</p>
  
  <pre><code>if(DEFINED BUILD_TESTS)
      add_subdirectory(tests)
  endif(DEFINED BUILD_TESTS)
  </code></pre>
  
  <p>Thanks 
  rG</p>