Tests live in two places:
- Cross-package suites under the root
tests/directory (contract, logs, config, integration, etc.). - Package-local suites under each workspace member's
tests/directory (e.g.packages/core/tests/,apps/gateway/tests/).
Pytest discovers both via testpaths = ["tests", "packages"] in pyproject.toml and resolves imports through the pythonpath list under [tool.pytest.ini_options], which already names every package's src/ directory.
Package-local test directories (packages/*/tests/, apps/*/tests/) must not contain an __init__.py.
The cross-package suites under the root tests/ tree do use __init__.py (one per subdirectory) because they form a coherent tests.* namespace.
Pytest is configured with --import-mode=importlib, so it does not require __init__.py to collect test modules. But mypy walks the directory tree by package name. Without --explicit-package-bases, two sibling __init__.py files named tests/__init__.py (e.g. packages/core/tests/__init__.py and apps/gateway/tests/__init__.py) both resolve to the top-level module name tests and collide:
apps/gateway/tests/__init__.py: error: Duplicate module named "tests"
(also at "packages/core/tests/__init__.py")
Mypy bails out on the duplicate before it checks any source code, which silently disables task lint / make lint for the whole repo. Omitting __init__.py from package-local test dirs sidesteps the collision without giving up strict mode anywhere else.
When adding a new package, scaffold its tests like this:
packages/my-pkg/
└── tests/
├── test_foo.py # no __init__.py here
└── test_bar.py
The existing pythonpath list in pyproject.toml already covers every workspace member's src/, so test modules can import rag_my_pkg directly without any additional configuration.