title: How to use xcodebuild with -only-testing and -skip-testing flag?
body: <p>I've noticed that there are two options in <code>xcodebuild</code>'s man page.</p>
  
  <pre><code>-only-testing:TEST-IDENTIFIER       
  </code></pre>
  
  <blockquote>
    <p>constrains testing by specifying tests to include, and excluding other tests</p>
  </blockquote>
  
  <pre><code>-skip-testing:TEST-IDENTIFIER       
  </code></pre>
  
  <blockquote>
    <p>constrains testing by specifying tests to exclude, but including other tests</p>
  </blockquote>
  
  <p>What I try:</p>
  
  <pre><code>xcodebuild -workspace MyWorkSpace.xcworkspace / 
  -sdk iphonesimulator / 
  -destination id=7F52F302-C6AF-4215-B269-39A6F9913D5B / 
  -scheme SCHEME-iOS / 
  test -only-testing:???
  </code></pre>
  
  <p>What is <code>TEST-IDENTIFIER</code> mean ?</p>