title: How to test if an object is a Stream in NodeJS
body: <p>I have a function which receives an object that could be a <code>string</code>, <code>Buffer</code> or <code>Stream</code>.</p>
  
  <p>I can easily test if the object is a Buffer like so:
  <code>if (x instanceof Buffer)</code></p>
  
  <p>What's the best way to test if an object is a Stream? There doesn't appear to be a Stream base class in node - is there?</p>
  
  <p>What should I look for?</p>