title: NoMethodError: undefined method `yesterday' for Date:Class
body: <p>Every answer posted on SO (yes, I checked) seems to have <code>require 'date'</code> as a solution. I've done that and my code still won't work.</p>
  
  <pre><code>require 'date'
  
  yesterday = RepSched::Helpers.datestring(Date.yesterday)
  </code></pre>
  
  <p>For some reason, Ruby chokes on Date.yesterday</p>
  
  <pre><code>NoMethodError: undefined method `yesterday' for Date:Class
  </code></pre>
  
  <p>What am I doing wrong?</p>
  
  <p><em>edit</em></p>
  
  <p>Oh no! Now my problem is bigger than I thought. Now that I've realized that issue, I realize DateTime's behavior is different too!</p>