Fix NullBooleanField deprecations in test suite

[rpkilby]

Supersedes #7432.

Merged the field behavior tests for NullBooleanField and nullable BooleanField, as NullBooleanField no longer has a distinct implementation. Added separate tests for the deprecation warning and disallowed allow_null argument.

[smithdc1]

How about something like this?

class TestNullBooleanField(TestCase):
    @pytest.mark.filterwarnings('ignore::rest_framework.RemovedInDRF314Warning')
    def test_allow_null(self):
        msg = '`allow_null` is not a valid option.'
        with self.assertRaisesMessage(AssertionError, msg):
            serializers.NullBooleanField(allow_null=False)

    def test_deprecation_warning(self):
        msg = "The `NullBooleanField` is deprecated"  # require full msg?
        with self.assertWarnsMessage(rest_framework.RemovedInDRF314Warning, msg):
            serializers.NullBooleanField()

Could also use the two assert....Message from pytest-django rather than subclassing from TestCase. 🤔

[rpkilby]

How have I never heard of assertWarns and assertWarnsMessage?? 😄 ✨

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[auvipy]

it is safe to close this now