Add failing test case for #3788

[flaiming]

Added failing test case for issue #3788. It tests that model's BooleanField default value (when True) is ignored on serializer.

[tomchristie]

The key here is that HTML forms do not provide a value when a boolean checkbox is left empty.
We have to treat empty as false, and provided as true - the model default isn't relevant in the context of HTML forms as there's no 'empty' state.

If you switch from using QueryDict to using a regular dictionary (ie the behavior you'd get if providing JSON input) then you'd get the behavior you'd expect.

Closing this, as the behavior is as described in the documentation.

http://www.django-rest-framework.org/api-guide/fields/#booleanfield

When using HTML encoded form input be aware that omitting a value will always be treated as setting a field to False, even if it has a default=True option specified. This is because HTML checkbox inputs represent the unchecked state by omitting the value, so REST framework treats omission as if it is an empty checkbox input.