We Replaced Jest With node:test in 12 Services — Here's What Broke and What Didn't

After months of using Jest for unit testing, we decided to take the plunge and migrate to the built-in node:test runner. The results were surprising, with some features working seamlessly and others requiring significant rework. In this post, we'll share our journey and the lessons we learned along the way. Introduction to node:test The node:test runner is a built-in testing framework that comes with Node.js. It's designed to be fast, efficient, and easy to use. Here's an example of a simple test using node:test: import { test } from ' node:test ' ; import { Command } from ' @aws-sdk/client-lambda ' ; test ( ' Lambda client test ' , async ( t ) => { const lambdaClient = new Command (); const response = await lambdaClient (); t . equal . responseStatusCode , 200 ; }); Warning: When using node:test, make sure to handle errors properly, as unhandled errors can cause the test runner to crash. Migrating from Jest to node:test Migrating from Jest to node:test requires some changes to your test code. One of the main differences is the way you handle ES modules. In Jest, you can use the jest.config.js file to configure how ES modules are handled. In node:test, you need to use the --test-type option to specify the type of test you're running. Here's an example of how to migrate a Jest test to node:test: // jest.test.js import { lambdaClient } from ' ../lambdaClient ' ; describe ( ' Lambda client test ' , () => { it ( ' should return 200 ' , async () => { const response = await lambdaClient (); expect ( response . statusCode ). toBe ( 200 ); }); }); // node-test.test.js import { test } from ' node:test ' ; import { lambdaClient } from ' ../lambdaClient ' ; test ( ' Lambda client test ' , async ( t ) => { const response = await lambdaClient (); t . equal ( response . statusCode , 200 ); }); Tip: Use the --coverage option to generate code coverage reports for your tests. Overcoming Incompatibilities and Limitations One of the main limitations of node:test is that it does not su