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

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

You can run with PYTHONPATH in project root

PYTHONPATH=. py.test

Or use pip install as editable import

pip install -e .   # install package using setup.py in editable mode

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.

I created this as an answer to your question and my own confusion. I hope it helps. Pay attention to PYTHONPATH in both the py.test command line and in the tox.ini.

https://github.com/jeffmacdonald/pytest_test

Specifically: You have to tell py.test and tox where to find the modules you are including.

With py.test you can do this:

PYTHONPATH=. py.test

And with tox, add this to your tox.ini:

[testenv]
deps= -r{toxinidir}/requirements.txt
commands=py.test
setenv =
    PYTHONPATH = {toxinidir}

I started getting weird ConftestImportFailure: ImportError('No module named ... errors when I had accidentally added __init__.py file to my src directory (which was not supposed to be a Python package, just a container of all source).

I was getting this error due to something even simpler (you could even say trivial). I hadn’t installed the pytest module. So a simple apt install python-pytest fixed it for me.

‘pytest’ would have been listed in setup.py as a test dependency. Make sure you install the test requirements as well.

Run pytest itself as a module with:
python -m pytest tests

This happens when the project hierarchy is, for example, package/src package/tests and in tests you import from src. Executing as a module will consider imports as absolute rather than relative to the execution location.

Recommended approach for pytest>=7: use the pythonpath setting

Recently, pytest has added a new core plugin that supports sys.path modifications via the pythonpath configuration value. The solution is thus much simpler now and doesn’t require any workarounds anymore:

pyproject.toml example:

[tool.pytest.ini_options]
pythonpath = [
  "."
]

pytest.ini example:

[pytest]
pythonpath = .

The path entries are calculated relative to the rootdir, thus . adds repo directory to sys.path in this case.

Multiple path entries are also allowed: for a layout

repo/
├── src/
|   └── lib.py
├── app.py
└── tests
     ├── test_app.py
     └── test_lib.py

the configuration

[tool.pytest.ini_options]
pythonpath = [
  ".", "src",
]

or

[pytest]
pythonpath = . src

will add both app and lib modules to sys.path, so

import app
import lib

will both work.

Original answer (not recommended for recent pytest versions; use for pytest<7 only): 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?

For me the problem was tests.py generated by Django along with tests directory. Removing tests.py solved the problem.

I got this error as I used relative imports incorrectly. In the OP example, test_app.py should import functions using e.g.

from repo.app import *

However liberally __init__.py files are scattered around the file structure, this does not work and creates the kind of ImportError seen unless the files and test files are in the same directory.

from app import *

Here’s an example of what I had to do with one of my projects:

Here’s my project structure:

microbit/
microbit/activity_indicator/activity_indicator.py
microbit/tests/test_activity_indicator.py

To be able to access activity_indicator.py from test_activity_indicator.py I needed to:

• start test_activity_indicatory.py with the correct relative import:

    from microbit.activity_indicator.activity_indicator import *

• put __init__.py files throughout the project structure:

    microbit/
    microbit/__init__.py
    microbit/activity_indicator/__init__.py
    microbit/activity_indicator/activity_indicator.py
    microbit/tests/__init__.py
    microbit/tests/test_activity_indicator.py

I had a similar issue. pytest did not recognize a module installed in the environment I was working in.

I resolved it by also installing pytest into the same environment.

I fixed it by removing the top-level __init__.py in the parent folder of my sources.

Very often the tests were interrupted due to module being unable to be imported.

After research, I found out that the system is looking at the file in the wrong place and we can easily overcome the problem by copying the file, containing the module, in the same folder as stated, in order to be properly imported.

Another solution proposal would be to change the declaration for the import and show MutPy the correct path of the unit. However, due to the fact that multiple units can have this dependency, meaning we need to commit changes also in their declarations, we prefer to simply move the unit to the folder.

According to a post on Medium by Dirk Avery (and supported by my personal experience) if you’re using a virtual environment for your project then you can’t use a system-wide install of pytest; you have to install it in the virtual environment and use that install.

In particular, if you have it installed in both places then simply running the pytest command won’t work because it will be using the system install. As the other answers have described, one simple solution is to run python -m pytest instead of pytest; this works because it uses the environment’s version of pytest. Alternatively, you can just uninstall the system’s version of pytest; after reactivating the virtual environment the pytest command should work.

I was having the same problem when following the Flask tutorial and I found the answer on the official Pytest documentation.
It’s a little shift from the way I (and I think many others) are used to do things.

You have to create a setup.py file in your project’s root directory with at least the following two lines:

from setuptools import setup, find_packages
setup(name="PACKAGENAME", packages=find_packages())

where PACKAGENAME is your app’s name. Then you have to install it with pip:

pip install -e .

The -e flag tells pip to install the package in editable or "develop" mode. So the next time you run pytest it should find your app in the standard PYTHONPATH.

I had the same problem in Flask.

When I added:

__init__.py

to the tests folder, the problem disappeared 🙂

Probably the application couldn’t recognize folder tests as a module.

My solution:

Create the conftest.py file in the test directory containing:

import os
import sys
sys.path.insert(0, os.path.dirname(os.path.realpath(__file__)) + "/relative/path/to/code/")

This will add the folder of interest to the Python interpreter path without modifying every test file, setting environment variable or messing with absolute/relative paths.

As pointed out by Luiz Lezcano Arialdi, the correct solution is to install your package as an editable package.

Since I am using Pipenv, I thought about adding to his answer a step-by-step how to install the current path as an edible with Pipenv, allowing to run pytest without the need of any mangling code or lose files.

You will need to have the following minimal folder structure (documentation):

package/
    package/
        __init__.py
        module.py
    tests/
        module_test.py
    setup.py

setup.py mostly has the following minium code (documentation):

import setuptools

setuptools.setup(name='package', # Change to your package name
                 packages=setuptools.find_packages())

Then you just need to run pipenv install --dev -e . and Pipenv will install the current path as an editable package (the –dev flag is optional) (documentation).

Now you should be able to run pytest without problems.

We have fixed the issue by adding the following environment variable.

PYTHONPATH=${PYTHONPATH}:${PWD}/src:${PWD}/test

Also if you run pytest within your virtual environment make sure pytest module is installed within your virtual environment. Activate your virtual environment and run pip install pytest.

It is a bit of a shame that this is an issue in Python… But just adding this environment variable is the most comfortable way, IMO:

export PYTHONPATH=$PYTHONPATH:.

You can put this line in you .zshrc or .bashrc file.

Since no one has suggested it, you could also pass the path to the tests in your pytest.ini file:

[pytest]
...
testpaths = repo/tests

See documentation: https://docs.pytest.org/en/6.2.x/customize.html#pytest-ini

Side effect for Visual Studio Code: it should pick up the unit test in the UI.

If this pytest error appears not for your own package, but for a Git-installed package in your package’s requirements.txt, the solution is to switch to editable installation mode.

For example, suppose your package’s requirements.txt had the following line:

git+https://github.com/foo/bar.git

You would instead replace it with the following:

-e git+https://github.com/foo/bar.git#egg=bar