title: test_func for UserPassesTestMixin with get_object does not work with ListView
body: <p>in the contacts section of the dashboard of my projects, saved contacts are only visible to the author but previously they are visible to everyone because I forgot to include <code>UserPassesTestMixin</code> in CBV. I included but browser showed me the error named NotImplemented test_func, I also implemented test_func </p>
  
  <p><strong>views.py</strong></p>
  
  <pre><code>class ContactListView(LoginRequiredMixin, UserPassesTestMixin, ListView):
     model = ClientContact
     template_name = 'site/contacts.html'
     context_object_name = 'contacts'
     ordering = ['created_at', '-updated_at']
  
     def test_func(self):
         contact = self.get_object()
         if self.request.user == contact.author:
            return True
         return False
  </code></pre>
  
  <p>it says again NotImplemented test_func, as well as get_oject, is an unresolved ref in ListView
  I am sure I am doing something wrong but I cannot find my mistake. Please if anyone who knows this, correct me! Thank you</p>