title: Python: Nose not picking up new test
body: <p>I have just added a unit test to one of my Python modules that nose is refusing to pick up. The test looks like this:</p>
  
  <pre><code>class TestMargin(unittest.TestCase):
  
      def setUp(self):
          super().setUp()
  
      def test_margin(self):
          self.assertTrue(False)
  </code></pre>
  
  <p>I would expect this test to fail but it seems it's not even picked up. I am running nose with the <code>--all-modules</code> flag, and tests in other modules are indeed being picked up so it doesn't seem to be a generic problem with nose. I have checked the documentation of nose and can't see any good reason why this test shouldn't work... </p>
  
  <p>EDIT: I fixed the problem by (somewhat haphazardly) adding an empty <code>__init__.py</code> at the level of the module. But why would this help?</p>