Скачать или смотреть How to Fix "Module Not Found" Errors in Python Unit Testing with pytest

Struggling with Python unit tests and facing "Module Not Found" errors? Discover how to resolve import issues in your project's structure for smoother testing with `pytest`.
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This video is based on the question https://stackoverflow.com/q/71738850/ asked by the user 'u84six' ( https://stackoverflow.com/u/455466/ ) and on the answer https://stackoverflow.com/a/71740065/ provided by the user 'Teejay Bruno' ( https://stackoverflow.com/u/13261176/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Navigating "Module Not Found" Errors in Python Unit Testing

If you're diving into Python and are eager to learn about testing, you might have already encountered some challenges along the way. One common problem that many beginners face is the "Module Not Found" error when running tests with frameworks like pytest (or unittest). This error often arises when your test files depend on other modules or files, and it can be frustrating when the documentation doesn’t seem to address your specific situation.

Understanding the Problem

In the example scenario, a user has created a simple project structure that looks like this:

[[See Video to Reveal this Text or Code Snippet]]

In my_app.py, they defined a function called say_hello which, at first, works perfectly fine. However, as soon as they introduce a new dependency by adding a function from my_lib.py, they encounter an error when running pytest:

[[See Video to Reveal this Text or Code Snippet]]

This confusion arises because even though both my_app.py and my_lib.py are in the same package, Python struggles to locate my_lib.py when called from the test file. So, what’s going wrong?

Why Does This Happen?

The main reason for this error is related to how Python handles imports. By default, Python considers the directory from which the script is run as the top-level directory for locating modules. Here’s a breakdown of common issues that might cause the "Module Not Found" error:

Working Directory: When you run tests from a particular directory, Python must know where to look for the modules.

Import Paths: Depending on how you structure your imports, Python may not be able to trace the path to the desired module.

Relative vs. Absolute Imports: You might be using an import style that isn’t compatible with your directory structure.

The Solution

To resolve this issue, you can modify the import statement in your my_app.py file to use an absolute import. Here’s the step-by-step solution:

Modify the Import Statement
Change the function import in my_app.py to use the absolute path. Instead of:

[[See Video to Reveal this Text or Code Snippet]]

Use:

[[See Video to Reveal this Text or Code Snippet]]

Test the Changes
After adjusting your import statement, try running your tests again using pytest. The new import should allow Python to correctly locate and load my_lib.py, resolving the "Module Not Found" error.

Consider Directory Structure
Ensure you're running pytest from the correct root directory (some_project in this case) so that Python knows where to find your modules. You can run your tests from the terminal like this:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

Unit testing is a powerful tool in Python that can enhance your code quality by allowing you to catch errors early. Understanding how Python handles imports is crucial for successfully running tests without running into errors. By using absolute imports and ensuring that your working directory is set correctly, you can sidestep the common pitfalls associated with module imports in your project.

Now you're better equipped to handle "Module Not Found" errors when testing with pytest. Happy coding and testing!