'An assertion is raised if the field name is unknown'

def test_unknown_field(self):

    for (prefix, kwargs) in self.msg_prefixes:
        with self.assertRaises(AssertionError) as cm:
            self.assertFormsetError(self.response_form_errors, u'my_formset', 0, u'Some_field', u'Some    error.', **kwargs)
        self.assertIn((prefix + u"The    formset    'my_formset',    form    0    in    context    0    does    not    contain    the    field    'Some_field'"), str(cm.exception))
