python - pytest cannot find module

Question

I am following the pytest good practices or at least I think I am. However, pytest cannot find my module. It seems not to include the current directory in its PYTHONPATH.

The source file:

def add(x, y):
    return x + y

The test file:

import pytest
from junk.ook import add


def test_add_true():
    assert add(1, 1) == 2

And the shell output with a Python 3 virtual environment called "p3".

p3; pwd          
/home/usr/tmp/junk
p3; ls           
total 0
0 junk/  0 tests/
p3; ls junk      
total 4.0K
4.0K ook.py     0 __init__.py
p3; ls tests 
total 4.0K
4.0K test_ook.py     0 __pycache__/
p3; pytest
============================= test session starts ==============================
platform linux -- Python 3.4.5, pytest-3.4.1, py-1.5.2, pluggy-0.6.0
rootdir: /home/usr/tmp/junk, inifile:
collected 0 items / 1 errors                                                   

==================================== ERRORS ====================================
______________________ ERROR collecting tests/test_ook.py ______________________
ImportError while importing test module '/home/usr/tmp/junk/tests/test_ook.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
tests/test_ook.py:2: in <module>
    from junk.ook import add
E   ImportError: No module named 'junk'
!!!!!!!!!!!!!!!!!!! Interrupted: 1 errors during collection !!!!!!!!!!!!!!!!!!!!
=========================== 1 error in 0.08 seconds ============================
    
    def test_add_true():
        assert add(1, 1) == 2

However, running the following does work fine.

p3; python -m pytest tests/
============================= test session starts ==============================
platform linux -- Python 3.4.5, pytest-3.4.1, py-1.5.2, pluggy-0.6.0
rootdir: /home/usr/tmp/junk, inifile:
collected 1 item                                                               

tests/test_ook.py .                                                      [100%]

=========================== 1 passed in 0.02 seconds ===========================

What am I doing wrong?

If you add __init__.py to the tests folder also, does it help? — DBedrenko
Adding a __init__.py in the tests directory did help. But now this introduces a subtle problem…. It should work without an __init__.py file. — Sardathrion - against SE abuse
What problem does it introduce? The article you linked puts __init__.py in the tests directory and all directories (that include tests) inside it recursively. — DBedrenko
But now this introduces a subtle problem: in order to load the test modules from the tests directory, pytest prepends the root of the repository to sys.path, which adds the side-effect that now mypkg is also importable. This is problematic if you are using a tool like tox to test your package in a virtual environment, because you want to test the installed version of your package, not the local code from the repository. — Sardathrion - against SE abuse
You have to install your package into your virtualenv. At least that's how I get rid of this error every time. — Mehdi Sadeghi

hoefling hoefling · Accepted Answer · 2018-02-28T16:13:48

Just put an empty conftest.py file in the project root directory:

$ pwd
/home/usr/tmp/junk
$ touch conftest.py

Your project structure should become:

junk
├── conftest.py
├── junk
│   ├── __init__.py
│   └── ook.py
└── tests
    └── test_ook.py

What happens here: when pytest discovers a conftest.py, it modifies sys.path so it can import stuff from the conftest module. So, since now an empty conftest.py is found in rootdir, pytest will be forced to append it to sys.path. The side effect of this is that your junk module becomes importable.

python - pytest cannot find module

2 Answers