test_try_2.py

class ProductQuestionnaireTestCase(TestCase):

    def test_vat_20_if_biscuit_coated_in_chocolate(self):
        product = ProductFactory()
        form = ProductQuestionnaireForm(data={
            'is_biscuit': True,
            'is_coated_in_chocolate': True
        })
        self.assertTrue(form.is_valid())
        form.save()
        product.refresh_from_db()
        self.assertEqual(product.vat, 20)