title: 'IntegrityError: column username is not unique' while using Django User model in test
body: <p>While running some tests, I started to get an IntegrityError in my setUp function. Here is my code:</p>
  
  <pre><code>def setUp(self):
      self.client = Client()
  
      self.emplUser = User.objects.create_user('employee@email.com', 'employee@email.com', 'nothing')
      self.servUser1 = User.objects.create_user('thebestcompany@email.com', 'thebestcompany@email.com', 'nothing')
      self.servUser2 = User.objects.create_user('theothercompany@email.com', 'theothercompany@email.com', 'nothing')
      self.custUser1 = User.objects.create_user('john@email.com', 'john@email.com', 'nothing')
      self.custUser2 = User.objects.create_user('marcus@email.com', 'marcus@email.com', 'nothing')
  
      ... save users here ...
  </code></pre>
  
  <p>Im wondering as to how this IntegrityError keeps getting raised. I delete all the users in the tearDown function and am using sqlite3 as my DB backend. I see no conflicting usernames and in production, I have no issues with using emails as usernames.</p>
  
  <p>This started happening only half an hour ago, out of the blue. Has anyone run into a solution to this problem?</p>