How to Mock a Local Function in Python Tests

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Mocking Local Functions in Python Testing

The Problem

You have a local function defined within your test case, and you want to verify if it's called correctly within the context of your test. This is a common scenario, especially when you want to separate concerns and keep your tests clean.

The Code Structure

Here’s an example representation of what you’re trying to achieve:

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The Issue

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This indicates that the mock patching is attempting to find a module that doesn't exist, as local functions cannot be referenced in this manner.

The Solution

To resolve this, you need to mock the local function directly, instead of trying to patch it as if it were part of a module. Below are the step-by-step instructions to achieve this.

Step-by-Step Guide

Import the Required Libraries: First, make sure you import the mock library from unittest.

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Define the Local Function as a Mock Object: Instead of defining the local function normally, you’ll define it as a Mock object.

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Create Your Handlers Dictionary: Map the action to your mocked function.

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Call the Function Under Test: Execute the code that should invoke the mocked function.

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Assert the Function Call: Finally, assert that your mocked function was called with the expected arguments.

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Final Implementation

Here’s how your complete test case would look:

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Conclusion

Try applying this in your own tests, and watch how it simplifies your testing process!