How Can I Fix 'ImportError: No Module Named...' Errors When Using pytest with a Hierarchical Project Structure?

Resolving PATH Issues for pytest with Module Import Errors

When using pytest to run tests on a project with a hierarchical file structure, you may encounter "ImportError: No module named ..." errors when importing modules from your application's path. This issue arises from the need to modify the sys.path to include the paths to the necessary modules.

Recommended Approach for pytest >= 7: pythonpath Setting

pytest versions 7 onwards offer a simplified solution using the pythonpath configuration value. This allows you to add specific paths to sys.path without the need for workarounds. In your configuration file (pyproject.toml or pytest.ini), you can specify the paths you want to include, like:

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

[pytest]
pythonpath = .

Original Answer for pytest < 7: conftest Solution

If you're using an older version of pytest (less than 7), you can use the empty conftest.py solution. This involves creating an empty conftest.py file in the project root directory. This triggers pytest to automatically add the parent directory of the conftest.py file to sys.path, resolving the import issues.

Explanation

Pytest scans for conftest modules during test collection to gather custom hooks and fixtures. To import custom objects from these modules, pytest adds the parent directory of conftest.py to sys.path.

Alternative Solutions

Additional solutions for this issue exist, depending on your project structure:

• Package Root Directory: Place the conftest.py file in the package root directory, which contains subpackages but is not a package itself (without an __init__.py file).
• src Layout: While possible to use with the src layout, placing conftest.py in the src directory may negate the benefits of the src layout. Instead, consider placing it in the package root directory.

Conclusion

By adjusting sys.path or using the conftest.py solution, you can resolve the "ImportError: No module named ..." errors and ensure successful test execution in your pytest environment.

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