title: Pytest assertion doesn't show differences on AssertionError
body: <p>I recently learned about using <em>Pytest</em> for doing unit tests in Python. I've played around with it in <a href="https://repl.it/" rel="noreferrer">Repl.it</a> by doing a simple assertion on two different strings which should fail.</p>
  
  <pre><code>import pytest
  assert 'a' == 'b'
  </code></pre>
  
  <p>Which fails with the error
  <code>
  Traceback (most recent call last):
    File "python", line 2, in &lt;module&gt;
  AssertionError
  </code></p>
  
  <p>However Pytest does not print 'a' or 'b'. This would be really helpful in debugging as I can compare the diff between 2 different strings. The <em>unittest</em> module has this feature by default. Does Pytest have this feature? If not how do I enable it? I'm using Pytest for a larger project and would love to figure this out before continuing work.</p>