title: How to test if a string is basically an integer in quotes using Ruby
body: <p>I need a function, <code>is_an_integer</code>, where</p>
  
  <ul>
  <li><code>"12".is_an_integer?</code> returns true.</li>
  <li><code>"blah".is_an_integer?</code> returns false.</li>
  </ul>
  
  <p>How can I do this in Ruby?  I would write a regex but I'm assuming there is a helper for this that I am not aware of.</p>