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

def test_unknown_field(self):

    for (prefix, kwargs) in self.msg_prefixes:
        msg = (prefix + "The    formset    'my_formset',    form    0    in    context    0    does    not    contain    the    field    'Some_field'")
        with self.assertRaisesMessage(AssertionError, msg):
            self.assertFormsetError(self.response_form_errors, 'my_formset', 0, 'Some_field', 'Some    error.', **kwargs)
