PATH issue with pytest 'ImportError: No module named YadaYadaYada' – Dev

The best answers to the question “PATH issue with pytest 'ImportError: No module named YadaYadaYada'” in the category Dev.

QUESTION:

I used easy_install to install pytest on a mac and started writing tests for a project with a file structure likes so:

repo/
   |--app.py
   |--settings.py
   |--models.py
   |--tests/
          |--test_app.py

run py.test while in the repo directory, everything behaves as you would expect

but when I try that same thing on either linux or windows (both have pytest 2.2.3 on them) it barks whenever it hits its first import of something from my application path. Say for instance from app import some_def_in_app

Do I need to be editing my PATH to run py.test on these systems? Has Anyone experienced this?

ANSWER:

conftest solution

The least invasive solution is adding an empty file named conftest.py in the repo/ directory:

$ touch repo/conftest.py

That’s it. No need to write custom code for mangling the sys.path or remember to drag PYTHONPATH along, or placing __init__.py into dirs where it doesn’t belong (using python -m pytest as suggested in Apteryx’s answer is a good solution though!).

The project directory afterwards:

repo
├── conftest.py
├── app.py
├── settings.py
├── models.py
└── tests
     └── test_app.py

Explanation

pytest looks for the conftest modules on test collection to gather custom hooks and fixtures, and in order to import the custom objects from them, pytest adds the parent directory of the conftest.py to the sys.path (in this case the repo directory).

Other project structures

If you have other project structure, place the conftest.py in the package root dir (the one that contains packages but is not a package itself, so does not contain an __init__.py), for example:

repo
├── conftest.py
├── spam
│   ├── __init__.py
│   ├── bacon.py
│   └── egg.py
├── eggs
│   ├── __init__.py
│   └── sausage.py
└── tests
     ├── test_bacon.py
     └── test_egg.py

src layout

Although this approach can be used with the src layout (place conftest.py in the src dir):

repo
├── src
│   ├── conftest.py
│   ├── spam
│   │   ├── __init__.py
│   │   ├── bacon.py
│   │   └── egg.py
│   └── eggs 
│       ├── __init__.py
│       └── sausage.py
└── tests
     ├── test_bacon.py
     └── test_egg.py

beware that adding src to PYTHONPATH mitigates the meaning and benefits of the src layout! You will end up with testing the code from repository and not the installed package. If you need to do it, maybe you don’t need the src dir at all.

Where to go from here

Of course, conftest modules are not just some files to help the source code discovery; it’s where all the project-specific enhancements of the pytest framework and the customization of your test suite happen. pytest has a lot of information on conftest modules scattered throughout their docs; start with conftest.py: local per-directory plugins

Also, SO has an excellent question on conftest modules: In py.test, what is the use of conftest.py files?

ANSWER:

I’m not sure why py.test does not add the current directory in the PYTHONPATH itself, but here’s a workaround (to be executed from the root of your repository):

python -m pytest tests/

It works because Python adds the current directory in the PYTHONPATH for you.

ANSWER:

Yes, the source folder is not in Python’s path if you cd to the tests directory.

You have 2 choices:

  1. Add the path manually to the test files, something like this:

    import sys, os
    myPath = os.path.dirname(os.path.abspath(__file__))
    sys.path.insert(0, myPath + '/../')
    
  2. Run the tests with the env var PYTHONPATH=../.

ANSWER:

I had the same problem. I fixed it by adding an empty __init__.py file to my tests directory.