How to Fix ModuleNotFoundError When Running Pytest in a /tests Directory

Learn how to resolve the `ModuleNotFoundError` in pytest when your tests are located in a `/tests` directory for a new Python project.
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Dealing with ModuleNotFoundError in Pytest

If you've started a new Python project and decided to introduce unit tests using pytest, you may encounter a frustrating issue: the ModuleNotFoundError. This is particularly common when your test files are organized within a /tests directory. In this post, we’ll identify the problem and guide you through the solution step-by-step.

The Problem

You might be facing an issue where pytest cannot find your module when executing tests. Here’s a typical scenario:

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This error can halt your progress and leave you puzzled about what went wrong.

Understanding the Cause

The root cause of this error usually stems from how Python resolves module paths. When you run pytest, it needs to know where to find your project's modules. If Python cannot locate your project structure, it raises the ModuleNotFoundError.

Common Reasons for the Error:

Incorrect Directory Structure: If Python's import path does not include your project's root directory.

PYTHONPATH Not Set: Often overlooked, the environment variable PYTHONPATH needs to be set to help Python locate the correct directories.

The Solution

To fix this issue, you need to ensure that Python knows where to find your project's root directory. Here’s how to do that:

Step 1: Set the PYTHONPATH Variable

When running tests, you can manually set the PYTHONPATH using the command line. This will inform Python where to find your modules.

Open your terminal.

Set the PYTHONPATH with the following command:

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Run your tests again using pytest.

Step 2: Verify Your Directory Structure

Ensure that your project directory is structured correctly. Here’s a recommended layout:

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The presence of __init__.py in both your main package (crmpicco) and your tests directory (tests) can help indicate that these are Python packages.

Step 3: Run the Tests

After setting the necessary environment variables and ensuring the directory structure is correct, proceed to run your tests again:

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Conclusion

By following these steps, you should be able to resolve the ModuleNotFoundError and successfully run your pytest tests. Remember, setting the PYTHONPATH is crucial when working with nested project structures. Now you can focus on writing and executing your tests without encountering module import issues.

If you continue to experience problems, review the directory paths and ensure every step has been followed correctly. Happy testing!