Fixed model_fields tests to use django TestCase.

        )

class DateTimeFieldTests(unittest.TestCase):

class DateTimeFieldTests(test.TestCase):

    def test_datetimefield_to_python_usecs(self):

        """DateTimeField.to_python should support usecs"""

        f = models.DateTimeField()

        self.assertEqual(obj.t, tim)

class BooleanFieldTests(unittest.TestCase):

class BooleanFieldTests(test.TestCase):

    def _test_get_db_prep_lookup(self, f):

        self.assertEqual(f.get_db_prep_lookup('exact', True, connection=connection), [True])

        self.assertEqual(f.get_db_prep_lookup('exact', '1', connection=connection), [True])

            self.assertFalse(boolean_field.has_default())

            b = BooleanModel()

            self.assertIsNone(b.bfield)

            with transaction.atomic():

                with self.assertRaises(IntegrityError):

                    b.save()

        finally: