title: How to check for instantiation of a python class during unit-tests
body: <p>I for the life of me can not remember how to test for the instination of a python class.</p>
  
  <p>It was something like:</p>
  
  <pre><code>try:
    m = MyModel()
  except:
    ...
  </code></pre>
  
  <p>I can't remember the exception to call or the assert to use. </p>