Why is my django unittest failing a constraint?

I have this model:

class TestopiaEvent(Model):
    event_id = AutoField(primary_key=True)
    name = CharField(max_length=255)
    start_date = DateField()
    end_date = DateField()
    testers_required = IntegerField()

    class Meta:
        constraints = [
            CheckConstraint(
                check=Q(start_date__lte=F('end_date'), start_date__gte=datetime.now().date()),
                name='correct_datetime'
            )
        ]

And this test:

class TestopiaEventTestCase(TestCase):
    def setUp(self):
        self.default_values = {
            'name': 'Testopia 1',
            'start_date': datetime.now().date(),
            'end_date': datetime.now().date() + timedelta(days=1),
            'testers_required': 1
        }
        self.testopia_event = TestopiaEvent(**self.default_values)

    def test_save_with_valid_model_check_database(self):
        self.assertIsNone(self.testopia_event.save())

And it fails with this error:

django.db.utils.IntegrityError: new row for relation "webserver_testopiaevent" violates check constraint "correct_datetime"
DETAIL:  Failing row contains (1, Testopia 1, 2020-07-24 00:00:00+00, 2020-07-25 00:00:00+00, 1).

I don’t understand why it is failing as it should only fail if today’s date is less than the start date and the start date or/and the start date is greater than the end date, which it isn’t?

What have I done wrong? Thanks

Edit: Here are the postgresdb constraints:

testopia=# d+ webserver_testopiaevent
Table

"public.webserver_testopiaevent"
      Column      |          Type          | Collation | Nullable |                          Default                          | Storage  | Stats target | Description 
------------------+------------------------+-----------+----------+-----------------------------------------------------------+----------+--------------+-------------
 event_id         | integer                |           | not null | nextval('webserver_testopiaevent_event_id_seq'::regclass) | plain    |              | 
 name             | character varying(255) |           | not null |                                                           | extended |              | 
 start_date       | date                   |           | not null |                                                           | plain    |              | 
 end_date         | date                   |           | not null |                                                           | plain    |              | 
 testers_required | integer                |           | not null |                                                           | plain    |              | 
Indexes:
    "webserver_testopiaevent_pkey" PRIMARY KEY, btree (event_id)
Check constraints:
    "correct_datetime" CHECK (start_date >= statement_timestamp() AND start_date <= end_date)
Access method: heap