              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(), [error])
 
</s> remove         self.assertEqual(field.check(), [
 </s> add         self.assertEqual(field.check(databases=self.databases), [ </s> remove         for db in connections:
            if router.allow_migrate(db, app_label, model_name=self.model._meta.model_name):
                return connections[db].validation.check_field(self, **kwargs)
        return []
 </s> add         errors = []
        for alias in databases:
            if router.allow_migrate(alias, app_label, model_name=self.model._meta.model_name):
                errors.extend(connections[alias].validation.check_field(self, **kwargs))
        return errors </s> remove                 model.check()
 </s> add                 model.check(databases={'default', 'other'}) </s> remove                 model.check()
 </s> add                 model.check(databases={'default', 'other'}) </s> remove     def _check_backend_specific_checks(self, **kwargs):
 </s> add     def _check_backend_specific_checks(self, databases=None, **kwargs):
        if databases is None:
            return []
            self.assertEqual(field.check(databases={'default'}), [error])
              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])
keep keep keep keep replace
 Fixed #31286 -- Made database specific fields checks databases aware.

Follow up to 0b83c8cc4db95812f1e15ca19d78614e94cf38dd. 
tests/invalid_models_tests/test_backend_specific.py