rescript-test VS rescript-jest

Besides bindings for JavaScript libraries, there is rescript-test - a lightweight test framework written in ReScript for ReScript. I have heard that some people like it, but for me, it lacks coverage output and Wallaby support.

As soon as you need to change the name or something, delete a field, or change a field… you’ve broken the API. This means you first need to change your Lambda(s) that use this new data, and ensure your unit tests (using ReTest) pass, and your integration tests (using Mocha & JavaScript) which invoke your Lambdas directly on a QA server still work.

To do that, we’re using rescript-test, which feels natural to those used to Jest, Mocha, etc. The only main difference is using testAsync vs test for async code, and having to define your own assertions vs. “Jest/Chai has ALL THE THINGS”.

Another popular option is to use bindings for Jest. However, in my opinion, Jest is a monstrous combine that is slow, has a hacky mock system, bad ESM support, and purely tries to mimic DOM API with JSDOM. AVA literally doesn't have any of these. Also, the available Jest bindings don't allow doing multiple assertions per test, which is often useful to me.

In order to write tests in ReScript, and thus test your code directly, you can use bs-jest, which provides ReScript bindings to Jest. If you prefer, you can also use the slightly less mature bs-mocha. You can also test the generated JavaScript or TypeScript files with no extra configuration.