title: setUpClass() missing 1 required positional argument: 'cls'
body: <p>I tried to use <code>setUpClass()</code> method for the first time in my life and wrote:</p>
  
  <pre><code>class TestDownload(unittest.TestCase):
  
      def setUpClass(cls):
          config.fs = True
  </code></pre>
  
  <p>and got: </p>
  
  <pre><code>Ran 0 tests in 0.004s
  
  FAILED (errors=1)
  
  Failure
  Traceback (most recent call last):
    File "/opt/anaconda3/lib/python3.5/unittest/suite.py", line 163, in _handleClassSetUp
      setUpClass()
  TypeError: setUpClass() missing 1 required positional argument: 'cls'
  </code></pre>
  
  <p>What does it mean and how to satisfy it?</p>