title: How to check if value is nan in unittest?
body: <p>I've got functions, which sometimes return NaNs with <code>float('nan')</code> (I'm not using numpy).</p>
  
  <p>How do I write a test for it, since</p>
  
  <pre><code>assertEqual(nan_value, float('nan'))
  </code></pre>
  
  <p>is just like <code>float('nan') == float('nan')</code> always false. Is there maybe something like <code>assertIsNan</code>? I could not find anything about it…</p>