How to run unitest from different directories with Python

Question

I have the following structure in my project;

project
    src
    ├── A.py
    └── B.py
    tests
    ├── test_b.py

and in B.py I import A.py like this;

from A import foo

B.py works fine when I run it. However when testing B.py in test_b.py I get an error saying

No module named A

I can make the test work with relative imports in B.py, but that fails when I run the module by itself.

Answer 1

Relative imports outside packages is a recipe for nightmares. Everything forks fine when you develop and test in the source directory. And problems start to occur as soon as you want to use your code from a different directory.

The workaround: Consistently add the directory of __file__ in sys.path before your local imports. As sys.path is a writable list, it will work. You should at least try to not add the directory if it is already present...

The idiomatic way: If you need local imports, then you probably need a package. It may require some work, because packages are expected to be installed , but it is a large + if you intend to later deploy your code. The downside, it that a package must be started as a module ( python -m xy ) and not as a plain script ( python x/y.py ). With your current structure, I would just add an empty __init__.py file in both src and tests folder, and add a __main__.py file in src if you want to lauch directly the package.

Then you should run everything (including tests and dev runs) from project: python -m src.B [params...] . Same thing for the tests python -m tests.test_b . Or directly (as the test folder and files start with test): python -m unittest discover