title: What is instrumentation in nyc istanbul?
body: <p>What is instumentation used in nyc? </p>
  
  <blockquote>
    <p>nyc's instrument command can be used to instrument source files outside of the context of your unit-tests:</p>
  </blockquote>
  
  <p>I assume it will do coverage outside unit-testing. I tried it with</p>
  
  <pre><code>nyc instrument src coverage/instrument
  </code></pre>
  
  <p>then run the application and tries hitting an endpoint</p>
  
  <pre><code>npm start
  </code></pre>
  
  <p>but when I do above, it doesn't generate a file in <code>nyc_output</code> thus can't report anything. </p>
  
  <p>Do I have to finish the <code>nyc instrument</code> command? how to do so? </p>