[Python] Prevent test functions from being bundled with Python package

I have a Python package (pyproject.toml setup with uv) and I would like to have unit-tests in the same file as the source code, leaving the tests/ directory exclusively for integration tests, similar to the way it is done in Rust with #[cfg(test)] modules.

I can do:

# add.py

def add(a, b):
return a + b

def test_add():
assert add(1, 2) == 3


Then uv run pytest can handle this and run the assertions.

However when I build the project, test_add is importable from module foo along with add.

How can I prevent this ?

Edit

I realise I can do:

if "pytest" in __import__("sys").modules:

def test_add():
assert add(1, 2) == 3


However this seems a bit brittle.

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