title: Assert called with argument of specific type
body: <p>I want to check in my test if a function is called with an argument of a specific class.</p>
  
  <pre><code>class Foo:
  ... 
  </code></pre>
  
  <p>I found mock.ANY, but there I cannot pass any class. What is want is:</p>
  
  <pre><code>test_mock.assert_called_with("expected string", ANY(spec=Foo))
  </code></pre>