Скачать или смотреть Testing a void Returning Function with Jest in TypeScript

Learn how to test a function that returns void using Jest in TypeScript, including handling retries and mock functions for effective error handling.
---
This video is based on the question https://stackoverflow.com/q/68492110/ asked by the user 'puggyman210' ( https://stackoverflow.com/u/15836698/ ) and on the answer https://stackoverflow.com/a/68492133/ provided by the user 'xdumaine' ( https://stackoverflow.com/u/381422/ ) 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: How to test a function that return void with Jest? Tyepscript

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 a void Returning Function with Jest in TypeScript

Testing asynchronous functions, especially those that return void, can be challenging, particularly when you want to implement retries upon failure. In this guide, we will walk through how to test a function that returns void using Jest in TypeScript. We will particularly focus on a use case which involves retrying a function call a certain number of times if it fails.

The Problem

You have a function called retryNTimes which is designed to retry executing another function a predefined number of times if it fails. However, when you attempt to test this function using Jest, you encounter a matcher error indicating that the received value must be a mock function.

Here's a snippet of the original retryNTimes function:

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

The Solution

To effectively test the retryNTimes function, we need to:

Mock the function that will be called within retryNTimes.

Handle asynchronous operations properly to account for functions that return promises.

Here’s how we can achieve this:

Step 1: Create a Mock Function

You need to create a mock function that simulates both a failure (throwing an error) and a success (returning void). You can use Jest’s mocking capabilities to do this. Here's an example of how to set up such a mock function:

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

Step 2: Modify the retryNTimes Function to Support Async

In your original implementation, the retryNTimes function does not wait for asynchronous operations to finish. This can be resolved by using async/await. Here’s an improved version of the function:

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

Step 3: Complete Test Cases

Now that you have mock functions and an updated retryNTimes, you can write your test cases effectively:

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

Conclusion

Testing functions in TypeScript that return void, especially those that wrap around retries and error handling, can be streamlined with proper use of Jest's mock functionalities and async capabilities. Remember, the keys to successful testing in these scenarios include creating effective mocks and handling asynchronous behavior accurately. By implementing these techniques, you can ensure that your functions behave as expected under various conditions.

If you're facing similar issues with Jest tests in TypeScript, we hope this guide has been helpful in providing clarity on setting up your tests!