Django: How to unit test Update Views/Forms

Question

I'm trying to unit test my update forms and views. I'm using Django Crispy Forms for both my Create and Update Forms. UpdateForm inherits CreateForm and makes a small change to the submit button text. The CreateView and UpdateView are very similar. They have the same model, template, and success_url. They differ in that they use their respective forms, and CreateView inherits django.views.generic.CreateView, and UpdateView inherits django.views.generic.edit.UpdateView.

The website works fine. I can create and edit an object without a problem. However, my second test shown below fails. How do I test my UpdateForm?

Any help would be appreciated. Thanks.

This test passes:

class CreateFormTest(TestCase):

    def setUp(self):
        self.valid_data = {
            'x': 'foo',
            'y': 'bar',
        }

    def test_create_form_valid(self):
        """ Test CreateForm with valid data """
        form = CreateForm(data=self.valid_data)
        self.assertTrue(form.is_valid())
        obj = form.save()
        self.assertEqual(obj.x, self.valid_data['x'])

This test fails:

class UpdateFormTest(TestCase):
    def setUp(self):
        self.obj = Factories.create_obj()  # Creates the object

    def test_update_form_valid(self):
        """ Test UpdateForm with valid data """
        valid_data = model_to_dict(self.obj)
        valid_data['x'] = 'new'
        form = UpdateForm(valid_data)
        self.assertTrue(form.is_valid())
        case = form.save()
        self.assertEqual(case.defendant, self.valid_data['defendant']

Answer 1

When pre-populating a ModelForm with an object that has already been created you can use the instance keyword argument to pass the object to the form.

form = SomeForm(instance=my_obj)

This can be done in a test, such as in the OP< or in a view to edit an object that has already been created. When calling save() the existing object will updated instead of creating a new one.