How to Fix Pytest's 'ImportError: No Module Named...' Issue?

Path Mishaps with Pytest: 'ImportError: No Module Named...'

When utilizing Pytest and encountering the vexing error 'ImportError: No module named...', the issue commonly stems from Python's module import behavior. Pytest traverses directories to locate modules, but when running outside the module's parent directory, it may fail to find them.

Recommended Approach for Recent Pytest Versions (>= 7)

Modern versions of Pytest offer a more straightforward solution via the 'pythonpath' configuration option. By defining 'pythonpath' in a 'pyproject.toml' or 'pytest.ini' file, you can add the necessary module directories to Python's search path.

Conftest Solution for Pytest

For older versions of Pytest, a less invasive approach involves creating an empty 'conftest.py' file in the root directory of your project. Pytest will automatically add this directory to Python's search path during test collection.

Tips for Specific Project Structures

• For package layouts without a parent directory containing an '__init__.py' file, place conftest.py in the package root directory.
• For projects utilizing the 'src' layout, place conftest.py in the 'src' directory. However, be cautious as this can compromise the benefits of the 'src' layout.

Conclusion

By modifying Python's search path using either the 'pythonpath' configuration or the 'conftest.py' file, you can resolve the 'ImportError: No module named...' issue and ensure smooth testing across different environments.

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