Repro issue 713

[prescod]

I built on Michel Samia's work to reformat into the format suggested by @blueyed.

#713

[blueyed]

That's a problem with pytest's saferepr not handling its own "Failed" exception, which is a BaseException (pytest-dev/pytest#6047).

Fixing that then shows this failure with your test:

============== test session starts ===============
platform linux -- Python 3.7.4, pytest-5.2.2.dev101+gf0c2b070c, py-1.7.0, pluggy-0.12.0 -- /home/daniel/Vcs/pytest-django/.venv/bin/python
cachedir: .pytest_cache
Django settings: tpkg.the_settings (from command line option)
rootdir: /tmp/pytest-of-daniel/pytest-8/test_migration_should_not_cause_internal_error0, inifile: tox.ini
plugins: forked-0.2, xdist-1.29.0, cov-2.6.1, django-3.6.1.dev1+ng2a93cd3.d20191018
collected 1 item

tpkg/test_the_test.py::test_inner_migrations Creating test database for alias 'default' ('/tmp/test_zawk6cdj_inner')...
Destroying old test database for alias 'default' ('/tmp/test_zawk6cdj_inner')...
Operations to perform:
  Apply all migrations: app, auth, contenttypes
Running migrations:
  Applying app.0001_initial... OK
  Applying app.0002_seed_data...ERROR

===================== ERRORS =====================
____ ERROR at setup of test_inner_migrations _____

request = <SubRequest '_django_db_marker' for <Function test_inner_migrations>>

    @pytest.fixture(autouse=True)
    def _django_db_marker(request):
        """Implement the django_db marker, internal to pytest-django.

        This will dynamically request the ``db``, ``transactional_db`` or
        ``django_db_reset_sequences`` fixtures as required by the django_db marker.
        """
        marker = request.node.get_closest_marker("django_db")
        if marker:
            transaction, reset_sequences = validate_django_db(marker)
            if reset_sequences:
                request.getfixturevalue("django_db_reset_sequences")
            elif transaction:
                request.getfixturevalue("transactional_db")
            else:
>               request.getfixturevalue("db")

/home/daniel/Vcs/pytest-django/pytest_django/plugin.py:511:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
/home/daniel/Vcs/pytest-django/pytest_django/fixtures.py:108: in django_db_setup
    **setup_databases_args
/home/daniel/Vcs/django/django/test/utils.py:173: in setup_databases
    serialize=connection.settings_dict.get('TEST', {}).get('SERIALIZE', True),
/home/daniel/Vcs/django/django/db/backends/base/creation.py:72: in create_test_db
    run_syncdb=True,
/home/daniel/Vcs/django/django/core/management/__init__.py:168: in call_command
    return command.execute(*args, **defaults)
/home/daniel/Vcs/django/django/core/management/base.py:369: in execute
    output = self.handle(*args, **options)
/home/daniel/Vcs/django/django/core/management/base.py:83: in wrapped
    res = handle_func(*args, **kwargs)
/home/daniel/Vcs/django/django/core/management/commands/migrate.py:233: in handle
    fake_initial=fake_initial,
/home/daniel/Vcs/django/django/db/migrations/executor.py:117: in migrate
    state = self._migrate_all_forwards(state, plan, full_plan, fake=fake, fake_initial=fake_initial)
/home/daniel/Vcs/django/django/db/migrations/executor.py:147: in _migrate_all_forwards
    state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
/home/daniel/Vcs/django/django/db/migrations/executor.py:245: in apply_migration
    state = migration.apply(state, schema_editor)
/home/daniel/Vcs/django/django/db/migrations/migration.py:124: in apply
    operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
/home/daniel/Vcs/django/django/db/migrations/operations/special.py:190: in database_forwards
    self.code(from_state.apps, schema_editor)
tpkg/app/migrations/0002_seed_data.py:9: in cb_seed_items
    Item.objects.get(name='This one is not there')
/home/daniel/Vcs/django/django/db/models/manager.py:82: in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <[Failed("Database access not allowed, use the "django_db" mark, or the "db" or "transactional_db" fixtures to enable it.") raised in repr()] QuerySet object at 0x7f99e78e7890>
args = ()
kwargs = {'name': 'This one is not there'}
clone = <QuerySet []>, limit = 21, num = 0

    def get(self, *args, **kwargs):
        """
        Perform the query and return a single object matching the given
        keyword arguments.
        """
        clone = self._chain() if self.query.combinator else self.filter(*args, **kwargs)
        if self.query.can_filter() and not self.query.distinct_fields:
            clone = clone.order_by()
        limit = None
        if not clone.query.select_for_update or connections[clone.db].features.supports_select_for_update_with_limit:
            limit = MAX_GET_RESULTS
            clone.query.set_limits(high=limit)
        num = len(clone)
        if num == 1:
            return clone._result_cache[0]
        if not num:
            raise self.model.DoesNotExist(
                "%s matching query does not exist." %
>               self.model._meta.object_name
            )
E           __fake__.Item.DoesNotExist: Item matching query does not exist.

/home/daniel/Vcs/django/django/db/models/query.py:414: DoesNotExist
============ short test summary info =============
ERROR tpkg/test_the_test.py::test_inner_migrations
=

[blueyed]

That's the crucial part, where pytest fails:

self = <[Failed("Database access not allowed, use the "django_db" mark, or the "db" or "transactional_db" fixtures to enable it.") raised in repr()] QuerySet object at 0x7f99e78e7890>

(this is fix the pending fix for pytest)

[blueyed]

So is that the issue then after all?
Or do you expect the test to behave different from raising "E fake.Item.DoesNotExist: Item matching query does not exist."?

[blueyed]

Followup in #777 (could not push here - see the checkbox on the right).