def test_inline_formset_factory(self):
        inlineformset_factory(Parent, Child, fk_name='mother', fields="__all__")
        inlineformset_factory(Parent, Child, fk_name='father', fields="__all__")
These should both work without a problem.
dataset/ETHPy150Open django/django/tests/inline_formsets/tests.py/InlineFormsetFactoryTest.test_inline_formset_factory