How to Create Incremental Fixture Values with Arguments in Pytest

Discover how to avoid repetitive fixture creation in Pytest by creating incremental fixture values using arguments effectively.
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This video is based on the question https://stackoverflow.com/q/68653661/ asked by the user 'MattSom' ( https://stackoverflow.com/u/6560773/ ) and on the answer https://stackoverflow.com/a/68656488/ 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.

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How to Create Incremental Fixture Values with Arguments in Pytest

When working with pytest, one common scenario arises when you have a fixture that needs to yield incremental values based on an input argument. For example, you might want to generate unique names each time you call a fixture, such as "Dummy Admin", "Dummy Admin_2", and so on. This guide will explore a solution to keep the input value persistent across multiple calls without creating new fixtures each time.

The Problem: Fixture Resetting

You may have encountered a situation where you define a fixture that generates names, but when you try to call that fixture multiple times with the same name, it resets the name each time. Here's an illustration of what this looks like:

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Output

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As shown, the output is not what we expect. The call to dummy_name with the same argument results in duplicated output, because each time we call it, it creates a new generator with the initial name.

The Solution: Using Callable Outside the Function

To overcome this limitation, you need to create an instance of the dummy_name fixture once, and then use that instance in your function calls. Here’s how you can do this effectively:

Step-by-Step Implementation

Define your fixture as usual.

Instantiate the fixture only once by calling it outside of the repeated calls.

Use the instantiated variable to call next() multiple times.

Here is the revised code:

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Expected Output

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With this approach, you’re effectively creating an incremental fixture that can maintain its state across multiple calls, without the need to redefine additional fixtures for every unique name.

Conclusion

Using pytest fixtures effectively can greatly enhance your testing strategy. By creating an instantiation of your fixture before utilizing it, you ensure that your inputs remain persistent across calls. This not only minimizes redundancy in your code but also creates a more organized testing structure.

Try implementing this method in your pytest tests, and enjoy smoother, more efficient testing!

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