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ImportError when using pytest in terminal [duplicate]

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, and 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. For instance, from app import some_def_in_app.
Do I need to be editing my PATH to run py.test on these systems?

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.

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?

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

Yes, the source folder is not in Python's path if you cd to the tests directory.
You have two choices:
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 + '/../')
Run the tests with the env var PYTHONPATH=../.

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.

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 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.

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

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).

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.

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 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.

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.

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

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 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.

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.

We have fixed the issue by adding the following environment variable.
PYTHONPATH=${PYTHONPATH}:${PWD}/src:${PWD}/test

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.

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

If nothing works, make sure your test_module.py is listed under the correct src directory.
Sometimes it will give ModuleNotFoundError not because modules are misplaced or export PYTHONPATH="${PWD}:${PYTHONPATH}" is not working, its because test_module.py is placed into a wrong directory under the tests folder.
it should be 1-to-1 mapping relation recursively instead of the root folder should be named as "tests" and the name of the file that include test code should starts with "test_",
for example,
./nlu_service/models/transformers.py
./tests/models/test_transformers.py
This was my experience.

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.

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.

ModuleNotFoundError with pytest

I want my tests folder separate to my application code. My project structure is like so
myproject/
myproject/
myproject.py
moduleone.py
tests/
myproject_test.py
myproject.py
from moduleone import ModuleOne
class MyProject(object)
....
myproject_test.py
from myproject.myproject import MyProject
import pytest
...
I use myproject.myproject since I use the command
python -m pytest
from the project root directory ./myproject/
However, then the imports within those modules fail with
E ModuleNotFoundError: No module named 'moduleone'
I am running Python 3.7 and have read that since 3.3, empty __init__ files are no longer needed which means my project becomes an implicit namespace package
However, I have tried adding an __init__.py file in myproject/myproject/ and also tried adding a conftest.py file in myproject/ but neither works
I have read answers that say to mess with the paths and then upvoted comments in other questions saying not to.
What is the correct way and what am I missing?
EDIT;
Possibly related, I used a requirements.txt to install pytest using pip. Could this be related? And if so, what is the correct way to install pytest in this case?
EDIT 2:
One of the paths in sys.path is /usr/src/app/ which is a docker volume lined to /my/local/path/myproject/.
Should the volume be /my/local/path/myproject/myproject/ instead?

Not sure if this solution was specific to my problem, but I simply add __init__.py to my tests folder and that solved the problem.

Solution: use the PYTHONPATH env. var
PYTHONPATH=. pytest
As mentioned by #J_H, you need to explicitly add the root directory of your project, since pytest only adds to sys.path directories where test files are (which is why #Mak2006's answer worked.)
Good practice: use a Makefile or some other automation tool
If you do not want to type that long command all the time, one option is to create a Makefile in your project's root dir with, e.g., the following:
.PHONY: test
test:
PYTHONPATH=. pytest
Which allows you to simply run:
make test
Another common alternative is to use some standard testing tool, such as tox.

Be sure to include . dot in the $PYTHONPATH env var.
Use $ python -m site, or this code fragment to debug such issues:
import pprint
import sys
pprint.pprint(sys.path)
Your question managed to use myproject at three different levels. At least during debugging you might want to use three distinct names, to reduce possible confusion.

In my case I added a __init__.py to my test directory with this inside it:
import sys
sys.path.append('.')
My app code is at the same level as my test directory.

In my case it is because I installed pytest on the system level but not in my virtual environment.
You can test this by python -m pytest. If you see ModuleNotFoundError: No module named 'pytest' then your pytest is at the system level.
Install pytest when the virtual environment is activated will fix this.

Kept everything same and just added a blank test file at the root folder .. Solved
Here are the findings, this problem really bugged me for a while.
My folder structure was
mathapp/
- server.py
- configuration.py
- __init__.py
- static/
- home.html
tests/
- functional
- test_errors.py
- unit
- test_add.py
and pytest would complain with the ModuleNotFoundError.
I introduced a mock test file at the same level as mathsapp and tests directory. The file contained nothing. Now pytest does not complain.
Result without the file
$ pytest
============================= test session starts =============================
platform win32 -- Python 3.8.2, pytest-5.4.2, py-1.8.1, pluggy-0.13.1
rootdir: C:\mak2006\workspace\0github\python-rest-app-cont
collected 1 item / 1 error
=================================== ERRORS ====================================
_______________ ERROR collecting tests/functional/test_func.py ________________
ImportError while importing test module 'C:\mainak\workspace\0github\python-rest-app-cont\tests\functional\test_func.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
tests\functional\test_func.py:4: in <module>
from mathapp.service import sum
E ModuleNotFoundError: No module named 'mathapp'
=========================== short test summary info ===========================
ERROR tests/functional/test_func.py
!!!!!!!!!!!!!!!!!!! Interrupted: 1 error during collection !!!!!!!!!!!!!!!!!!!!
============================== 1 error in 0.24s ===============================
Results with the file
$ pytest
============================= test session starts =============================
platform win32 -- Python 3.8.2, pytest-5.4.2, py-1.8.1, pluggy-0.13.1
rootdir: C:\mak2006\workspace\0github\python-rest-app-cont
collected 2 items
tests\functional\test_func.py . [ 50%]
tests\unit\test_unit.py . [100%]
============================== 2 passed in 0.11s ==============================

Better Solution
Try adding a single __init__.py to your tests directory (a level up from your module) with this contents:
import sys
sys.path.append('.')
sys.path.append('./my_module')
Your file structure should look like this:
project
my_module
package.py
tests
__init__.py
my_tests.py
The first append to sys.path will enable you to import from <your-module-name> and the second will enable your packages to import as normal.
In your tests you can import by using from my_module.package import function whereas in your module import using simply from package import function.
Edit: Seems like this solution is not universal (like the others).
I was able to solve this issue using help from this answer.
Add an __init__.py to your main module directory that contains
import pathlib, sys
sys.path.append(str(pathlib.Path(__file__).parent))
I also added another __init__.py to my tests directory (thanks to this answer) with
import sys
sys.path.append('.')

So it seems that the sys.path has to include the application directory rather than the project root folder containing the application directory and test directory.
So in my case /my/local/path/myproject/myproject/ had to be in sys.path rather than /my/local/path/myproject/.
Then I could run pytest in /my/local/path/myproject/ (didn't need python -m pytest). This meant that the modules within /myproject/myproject/ could find each other and the tests as well without any namespace nesting.
So my tests looked like
from moduleone import ModuleOne
import pytest
def test_fun():
assert ModuleOne.example_func() == True
That said, there seem to be many gotchas, so I have no idea if this is correct..

I suggest you have a code structure like this:
myproject/
helpers/
moduleone.py
moduletwo.py
tests/
myproject_test.py
conftest.py
And the content of conftest.py file is:
pytest_plugins = ['helpers']
Run pytest again.

Using poetry and pytest 5.4.3, I had the following structure (some folders / files have been removed for clarity):
project structure
.
├── my_app
│   ├── __init__.py
│   ├── main.py
│   ├── model.py
│   └── orm.py
├── poetry.lock
├── pyproject.toml
├── README.rst
└── tests
├── __init__.py
├── conftest.py
├── test_my_app.py
└── utilities
└── db_postgresql_inmemory.py
tests/conftest.py
pytest_plugins = [
"utilities.db_postgresql_inmemory",
]
which generated a module not found error for the fixture:
ImportError: Error importing plugin "utilities.db_postgresql_inmemory": No module named 'utilities'
None of the other answers have worked for me, as I have tried to add:
[me#linux ~/code/my_app]touch tests/utilities/__init__.py
[me#linux ~/code/my_app]touch ./test_blank.py
I could make the import from conftest.py work by REMOVING both __init__.py files:
[me#linux ~/code/my_app]rm tests/utilities/__init__.py tests/__init__.py

In 2023.02, according to the document of pytest, you can simply add following config to your pyproject.toml to solve this problem
[tool.pytest.ini_options]
pythonpath = "src"
addopts = [
"--import-mode=importlib",
]

I ran into this issue as well and am using poetry for dependency management and direnv for my project specific environment variables. Please note, I am relatively new to Python so I don't know if this is the correct fix.
Here is my entire .envrc file:
layout_poetry() {
if [[ ! -f pyproject.toml ]]; then
log_error 'No pyproject.toml found. Use `poetry new` or `poetry init` to create one first.'
exit 2
fi
local VENV=$(poetry env list --full-path | cut -d' ' -f1)
if [[ -z $VENV || ! -d $VENV/bin ]]; then
log_error 'No created poetry virtual environment found. Use `poetry install` to create one first.'
exit 2
fi
VENV=$VENV/bin
export VIRTUAL_ENV=$(echo "$VENV" | rev | cut -d'/' -f2- | rev)
export POETRY_ACTIVE=1
PATH_add "$VENV"
}
layout poetry
export PYTHONDONTWRITEBYTECODE=1
export PYTHONPATH="$PWD/project_name"
I don't know if I need to layout poetry because it is supposed to be creating virtual environments for us already but this is what I coworker recommended so I went with it. Layout poetry also didn't work without that function and it didn't like when I added it to my zshenv so I added it here.
For this specific question, the last line is the money maker.

ANOTHER SUGGESTION
See this answer: https://stackoverflow.com/a/69691436/595305

I was facing the issue which i resolved by
Installing pytest at the root of my project using pip install pytest
Adding blank __init__.py in the sibling of my test_file.py which i wanted to execute.

I have resolved it by adding export PYTHONPATH="your root dir/src"
i.e.
export PYTHONPATH="/builds/project/src"
poetry run pytest .....

The simplest solution I found was to manually add my target module to syspath. Lets say you have a structure like this:
flaskapp
- src
-- app.py
-- utils
-- ...
- tests
docs
venv
This makes my test folder a sibling to my module's src folder. If I start putting test_* files that need to import some of the module's code, I can simply:
import src.utils.calculator
And this would be fine until I try to import a file that imports another file from the module. The solution is simple: add a __init__.py to your tests folder, and put this line inside:
import sys, os
sys.path.insert(0, os.path.abspath(os.path.join(os.path.dirname(__file__), '../src')))
And just modify the last part relative to your module location and folder name

For me, when I was checking my project structure I found parent directory and sub directory having same names. When I changed the directory name, I got it working. So,
# Did not work
- same_name_project/
- same_name_project/
- tests/
# Worked
- different_named_project/
- a_unique_directory/
- tests/

How does one handle multiple modules/packages in python?

I've spent hours researching this problem, and I'm still baffled. Please find my ignorance charming.
I'm building a python program that will allow me to pit two AIs against each other in a game of battleship.
Here's my directory structure:
.
├── ais_play_battleship
│   ├── game.py
│   ├── __init__.py
│   ├── player.py
│   └── ship.py
├── LICENSE
├── README.md
└── tests
└── ship_test.py
2 directories, 7 files
Currently, I'm trying to write ship_test.py, but I cannot seem to import ais_play_battleship.ship. I get the dreaded "ModuleNotFoundError"
Here's what my research has taught me about my problem:
If you want to import python code from another directory, you should make that directory a package instead of a module. Therefore, I've placed an __init__.py file in the root of ais_play_battleship.
Python will only search the directory python is launched from as well as the directory of the script you're running. Therefore, I've been trying to launch my tests by running python3 tests/ship_tests.py from the root directory.
Here are my specific questions:
Why is the error a "ModuleNotFound" error? Shouldn't it be "PackageNotFound"?
Am I correct to make ais_play_battleship a package?
How can I keep my tests in a separate directory and still use the code in ais_play_battleship?
Please forgive me, as I'm not very good at asking questions on StackOverflow. Please tell me how I can improve.

I am answering my own question, as I haven't yet received a satisfactory answer. The best resource I've found is available here. In summary:
Python does NOT search the directory you run python from for modules. Furthermore, adding an __init__.py file to make a directory a package is not enough to make it visible to an instance of python running in another folder. You must also install that package. Therefore, the only two ways to access a module in another directory are:
Install the packaged module in site-packages (this requires the creation of a setup.py file and installation using pip install . More information is available here.
Modify path to resolve the module
I ended up settling with the second option, for reasons discussed below.
The first option requires one to reinstall the package at every change to a package. This is difficult on a constantly-changing codebase, but can be made easier by using build automation. However, I'd like to avoid this added complexity.
I shied away from the second option for a long time, because it seemed that modifying the path would require hard-coding the absolute path to my module, which is obviously unacceptable, as every developer would have to edit that path to fit their environment. However, this guide provides a solution to this problem. Create a ./tests/context.py file with the following contents:
import os
import sys
sys.path.insert(0, os.path.abspath(os.path.join(os.path.dirname(__file__), '..')))
Then, in my ship_test.py module, I imported the context and the module I needed:
import context
import ais_play_battleship.ship
# (I include the submodule ship because ais_play_battleship itself does not have
# any attributes or methods, and the submodule ship is the only one I am testing
# in ship_test.py)
This fits my project better, because it works as expected without having to worry about installing my package (or the method by which my package was installed).

To solve this problem without relying on hacking about your sys.path, create a setup.py file and as a build step for your test runner, have it run pip install . first. You might want to use a tool like tox.
In the top level directory:
setup.py
from setuptools import setup
setup(name='ais_play_battleship')
tox.ini
[tox]
envlist = py36, py37
[testenv]
deps=pytest
commands=
pip install . --quiet
py.test -q
then run your tests (in this example we use tox to do this so that we can also configure how the test environment can be configured) : tox

Run tests/ship_test.py as a module
python -m tests.ship_test

How to run tests without installing package?

I have some Python package and some tests. The files are layed out following http://pytest.org/latest/goodpractices.html#choosing-a-test-layout-import-rules
Putting tests into an extra directory outside your actual application
code, useful if you have many functional tests or for other reasons
want to keep tests separate from actual application code (often a good
idea):
setup.py # your distutils/setuptools Python package metadata
mypkg/
__init__.py
appmodule.py
tests/
test_app.py
My problem is, when I run the tests py.test, I get an error
ImportError: No module named 'mypkg'
I can solve this by installing the package python setup.py install but this means the tests run against the installed package, not the local one, which makes development very tedious. Whenever I make a change and want to run the tests, I need to reinstall, else I am testing the old code.
What can I do?

I know this question has been already closed, but a simple way I often use is to call pytest via python -m, from the root (the parent of the package).
$ python -m pytest tests
This works because -m option adds the current directory to the python path, and hence mypkg is detected as a local package (not as the installed).
See:
https://docs.pytest.org/en/latest/usage.html#calling-pytest-through-python-m-pytest

The normal approach for development is to use a virtualenv and use pip install -e . in the virtualenv (this is almost equivalent to python setup.py develop). Now your source directory is used as installed package on sys.path.
There are of course a bunch of other ways to get your package on sys.path for testing, see Ensuring py.test includes the application directory in sys.path for a question with a more complete answer for this exact same problem.

On my side, while developing, I prefer to run tests from the IDE (using a runner extension) rather than using the command line. However, before pushing my code or prior to a release, I like to use the command line.
Here is a way to deal with this issue, allowing you to run tests from both the test runner used by your IDE and the command line.
My setup:
IDE: Visual Studio Code
Testing: pytest
Extension (test runner): https://marketplace.visualstudio.com/items?itemName=LittleFoxTeam.vscode-python-test-adapter
Work directory structure (my solution should be easily adaptable to your context):
project_folder/
src/
mypkg/
__init__.py
appmodule.py
tests/
mypkg/
appmodule_test.py
pytest.ini <- Use so pytest can locate pkgs from ./src
.env <- Use so VsCode and its extention can locate pkgs from ./src
.env:
PYTHONPATH="${PYTHONPATH};./src;"
pytest.ini (tried with pytest 7.1.2):
[pytest]
pythonpath = . src
./src/mypkg/appmodule.py:
def i_hate_configuring_python():
return "Finally..."
./tests/mypkg/appmodule_test.py:
from mypkg import app_module
def test_demo():
print(app_module.i_hate_configuring_python())
This should do the trick

Import the package using from .. import mypkg. For this to work you will need to add (empty) __init__.py files to the tests directory and the containing directory. py.test should take care of the rest.

Py.test No module named *

I have a folder structure like this
App
--App
--app.py
--Docs
--Tests
--test_app.py
In my test_app.py file, I have a line to import my app module. When I run py.test on the root folder, I get this error about no module named app. How should I configure this?

Working with Python 3 and getting the same error on a similar project layout, I solved it by adding an __init__ file to my tests module.
$ touch tests/__init__.py
I'm not great at packaging and importing, but I think that this helps pytest work out where the target App module is located.

I already had an __init__.py file in the /App/App directory and wanted to run tests from the project root without any path-mangling magic:
python -m pytest tests
The output immediately looks like this:
➟ python -m pytest tests
====================================== test session starts ======================================
platform linux -- Python 3.5.1, pytest-2.9.0, py-1.4.31, pluggy-0.3.1
rootdir: /home/andrew/code/app, inifile:
plugins: teamcity-messages-1.17
collected 46 items
... lines omitted ...
============================= 44 passed, 2 skipped in 1.61 seconds ==============================

I had a similar problem and had to delete __init__.py from the root and add an __init__.py to the tests folder.

So you are running py.test from /App. Are you sure /App/App is in your $PYTHONPATH?
If it's not, code that tries to import app will fail with such a message.
EDIT0: including the info from my comment below, for completeness.
An attempt to import app will only succeed if it was executed inside /App/App, which is not the case here. You probably want to make /App/App a package by putting __init__.py inside it, and change your import to qualify app as from App import app.
EDIT1: by request, adding further explanation from my second comment below.
By putting __init__.py inside /App/App, that directory becomes a package. Which means you can import from it, as long as it - the directory - is visible in the $PYTHONPATH. I.e. you can do from App import app if /App is in the $PYTHONPATH. Your current working directory gets automatically added to $PYTHONPATH, so when you run a script from /App, the import will work.

Running pytest with the python -m pytest command helps with this exact thing.
Since your current package is not yet in your $PYTHONPATH or sys.path - pytest gets this error.
By using python -m pytest you automatically add the working directory into sys.path for running pytest. Their documentation also mentions:
This is almost equivalent to invoking the command line script pytest

I also got same error while running test cases for my app located as below
myproject
--app1
--__init.py__
--test.py
--app2
--__init.py__
--test.py
--__init.py__
I deleted my myproject's init.py file to run my test cases.

TL;DR
You might as well add an empty conftest.py file to your root app folder.
(if you take a look at the question folder structure, that would be the same level as the "Tests" folder, not inside of it).
More info:
Pytest looks for conftest.py files inside all your project folders.
conftest.py provides configuration for the file tree pytest finds it in. Because pytest somehow scans all subdirectories starting from conftest.py folder, it should find packages/modules outside the tests folder (as long as a conftest.py file is in your app root folder).
Eventually, you might want to write some code in your empty conftest.py, specially to share fixtures among different tests files, in order to avoid duplicate code. Afterall, the DRY principle (Don't Repeat Yourself) should also be follwed when writing tests.
Adding __init.py__ to the tests folder also should help pytest to find modules throughout your application. However, note that Python 3.3+ has implicit namespace packages that allow it to create a packages without an __init__.py file. That been said, creating __init__.py files for this specific purpose seems more like a a workaround for pytest than a python requirement. More about that in: Is __init__.py not required for packages in Python 3.3+

I got the similar issue. And after trying multiple things including installing pytest on virtual environment and adding/removing __init__.py file from the package, none worked for me.
Solution that worked for me is(windows solution):
Added Project folder(not package folder) to python path(set PYTHONPATH=%PYTHONPATH%;%CD%)
Ran my script from Project Folder and boom, it worked.

I hit the same issue.
my-app
--conf
--my-app
--tests
I set the __init__.py files. I added a conftest.py ( for sharing pytest.fixtures ). I added this to my Poetry file ( pyproject.toml:
[tool.pytest.ini_options]
pythonpath = [
"."
Turned out it was my use of hyphens and not underscores ! Noo...
# pytest can't find Module
--my-app
# works
--my_app

What worked for me: I had to make absolute imports in my test file and call python -m test in the root folder.

This worked for me:
Went to parent app, and pip install -e . (install a local and editable app).