Скачать или смотреть How to Test Constants Declarations with pytest in Python

Discover how to effectively test constant declarations in Python using `pytest`. Learn about monkeypatching and reloading modules to ensure your tests return the expected values.
---
This video is based on the question https://stackoverflow.com/q/66782316/ asked by the user 'Gatmando' ( https://stackoverflow.com/u/149154/ ) and on the answer https://stackoverflow.com/a/66788289/ provided by the user 'MrBean Bremen' ( https://stackoverflow.com/u/12480730/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Testing constants declarations using pytest

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Testing Constants Declarations Using Pytest

When developing applications in Python, you often set up constants to hold fixed values. However, testing these constants can become tricky, especially if they rely on environment variables. If you are facing issues with asserting these constants in your tests, you’re not alone. This post will dive into a common scenario and provide a straightforward solution to ensure your tests run smoothly.

The Problem at Hand

Imagine you have a Python application that defines constants in a constants.py file. For example, you declare:

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

In your test file, you aim to check if this constant correctly reflects the value from the environment variable. Here’s a snippet of what your test might look like:

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

In this test case, the first assertion passes, but the second one fails, indicating that constants.APP_CONSTANT_1 results in None. This issue arises because constants.py is loaded at an earlier stage in the testing process, and by the time your test runs, the environment variable hasn’t been updated.

The Solution: Reloading the Constants

To tackle this challenge and correctly test your constants, you can reload the constants module after setting the environment variable. Here's how to implement this fix:

Step-by-Step Guide

Import the Necessary Modules:
Make sure to import os, reload from importlib, and your constants module.

Set up Your Monkeypatch Fixture:
Use the monkeypatch fixture to set the environment variable correctly and reload your constants.

Adjust Your Test Method:
Modify the test to use the reloaded module:

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

Explanation of Changes

Using monkeypatch.setenv: This method allows you to set just the required environment variable without affecting others. It's cleaner and more specific than using monkeypatch.setattr.

Reloading constants: By reloading the module, you ensure that it picks up the new value from the environment variable you set, allowing the assertions to pass successfully.

Conclusion

By simply reloading the constants module after setting your environment variables, you can effectively test constant values without running into issues. This technique will not only streamline your tests but also enhance the reliability of your application configuration.

With this knowledge, you should feel empowered to tackle any similar problems in your tests using pytest. Happy coding!