from unittest import mock

from django.core.checks import Error

from django.db import connections, models

from django.test import SimpleTestCase

from django.test.utils import isolate_apps

def dummy_allow_migrate(db, app_label, **hints):

    # Prevent checks from being run on the 'other' database, which doesn't have

    # its check_field() method mocked in the test.

    return db == "default"

@isolate_apps("invalid_models_tests")

class BackendSpecificChecksTests(SimpleTestCase):

    @mock.patch("django.db.models.fields.router.allow_migrate", new=dummy_allow_migrate)

    def test_check_field(self):

        """Test if backend specific checks are performed."""

        error = Error("an error")

        class Model(models.Model):

            field = models.IntegerField()

        field = Model._meta.get_field("field")

        with mock.patch.object(

            connections["default"].validation, "check_field", return_value=[error]

        ):

            self.assertEqual(field.check(databases={"default"}), [error])