test_add and required form fields, usch as django-treebeard's _position

[jayvdb]

When trying to add tests to django-oscar, I am running into a problem with a model which uses https://github.com/django-treebeard/django-treebeard

First I need to map its slug field

from model_bakery import baker
from model_bakery.generators import default_mapping, SlugField

baker.generators.add('oscar.models.fields.slugfield.SlugField', default_mapping[SlugField])

Then the test_add fails

FAIL: test_add (oscar.apps.catalogue.tests.test_admin.CategoryAdminTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/lib/python3.8/site-packages/admin_auto_tests/test_model.py", line 123, in test_add
    self.assertEqual(len(response.context_data['errors']), 0,
AssertionError: 1 != 0 : _position: This field is required.

The _position feel is a required ChoiceField on the form.

I see model-bakery (and mommy) doesnt mentions support for ChoiceField, so I add _position using the create_form_instance_data hook (nice!)

This is a forms field, not a db field, which might account for bakery not supporting it.
I'll also raise an issue there.

If there isnt opportunity to add support for form fields to bakery, perhaps django-admin-auto-tests should detect required form fields and mark the test as a skip or fail with a better explanation of how to implement create_form_instance_data.