I recently upgraded my Django dependency to 4.2, and now running tests via Tox fails with:

ModuleNotFoundError: No module named 'mypackage'

I haven’t changed anything else and running Tox for Django 3.2 works fine.

My tox.ini looks like:

[tox]
envlist = py{38}-django{32,42}
recreate = True

[testenv]
basepython =
    py38: python3.8
deps =
    -r{toxinidir}/requirements.txt
    -r{toxinidir}/requirements-test.txt
    django32: Django>=3.2,<3.3
    django42: Django>=4.2,<5.0
    -e .  # Install the current package in editable mode
commands = django-admin.py test --traceback --settings=mypackage.tests.settings mypackage.tests.tests.TestCase

and my project structure looks like:

myproject/
├── myproject/
│   ├── __init__.py
│   ├── tests/
│   │   ├── __init__.py
│   │   ├── settings.py
│   │   └── tests.py
│   └── ...
├── .tox/
├── .env/
├── .git/
├── setup.py
├── requirements.txt
├── requirements-test.txt
├── tox.ini
└── ...

and my test settings look like:

import os

PROJECT_DIR = os.path.dirname(__file__)

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': ':memory:',
    }
}

ROOT_URLCONF = 'mypackage.tests.urls'

INSTALLED_APPS = [
    'django.contrib.auth',
    'django.contrib.admin',
    'django.contrib.contenttypes',
    'django.contrib.messages',
    'django.contrib.sessions',
    'django.contrib.sites',
    'mypackage',
    'mypackage.tests',
    'admin_steroids',
]

MEDIA_ROOT = os.path.join(PROJECT_DIR, 'media')

USE_TZ = True

TIME_ZONE = 'America/New_York'

USE_DEPRECATED_PYTZ = True

AUTH_USER_MODEL = 'auth.User'

SECRET_KEY = 'abc123'

SITE_ID = 1

BASE_SECURE_URL = 'https://localhost'

BASE_URL = 'http://localhost'

MIDDLEWARE_CLASSES = MIDDLEWARE = (
    'django.middleware.common.CommonMiddleware',
    'django.contrib.sessions.middleware.SessionMiddleware',
    'django.middleware.csrf.CsrfViewMiddleware',
    'django.contrib.auth.middleware.AuthenticationMiddleware',
    'django.contrib.messages.middleware.MessageMiddleware',
    'django.middleware.locale.LocaleMiddleware',
)

TEMPLATES = [
    {
        'BACKEND': 'django.template.backends.django.DjangoTemplates',
        'DIRS': [
            '%s/../templates' % PROJECT_DIR,
            '%s/../static' % PROJECT_DIR,
        ],
        'OPTIONS': {
            'context_processors': [
                'django.contrib.auth.context_processors.auth',
                'django.template.context_processors.debug',
                'django.template.context_processors.request',
                'django.template.context_processors.i18n',
                'django.template.context_processors.media',
                'django.template.context_processors.static',
                'django.template.context_processors.tz',
                'django.contrib.messages.context_processors.messages',
            ],
            'loaders': [
                'django.template.loaders.filesystem.Loader',
                'django.template.loaders.app_directories.Loader',
            ],
            'debug':
            True,
        },
    },
]

I don’t see anything in the Django ~4 release notes that look like they would effect how Django detects packages.

I also checked in the generated .tox/py38-django42/lib/python3.8/site-packages and mypackage exists in there, so it should be detectable like any other package.

What am I doing wrong?