How to Mock ES6 Imported Functions in Node.js with Jest

---

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: Can't mock a ES6 imported function in NodeJS

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

The Problem: Mocking an ES6 Imported Function

Scenario: You have an ES6 module containing a function named fetchLiveMatches, which fetches data from an external API using Axios. You want to test a controller function that uses this service but are encountering issues when trying to mock the fetchLiveMatches function in a Jest test case.

Here's a snippet of the problematic test code:

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

When running the test, Jest throws an error indicating that it cannot treat fetchLiveMatches as a mock function. This is a common pitfall when you involve ES6 modules without the right configuration.

The Solution: Using Dynamic Imports and Unstable Mocking

The solution involves adapting your test to dynamically import your modules after setting up the mocks. Here's how to implement it step by step:

Step 1: Change Your Mocking Strategy

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

Step 2: Import Your Modules Dynamically

After you’ve set up your mock, you then import your controller and service modules within the test scope. This is important so the mocks are in effect before the module's functions are called.

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

Step 3: Prepare Your Test Environment

Set up your request, response, and next functions as you did previously, then run your test:

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

Complete Test Example

Putting it all together, your updated test case should look like this:

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

Conclusion

By employing these techniques, you can enhance your testing strategy, maintain cleaner code, and ultimately execute more reliable tests. Happy testing!