rescript-promise VS rescript-test

We need the Promise library as it is the best way to use Promises in ReScript. We utilize the Jzon library for deterministically parsing our JSON into sound ReScript types without using the super verbose Js.Json classify syntax. Finally, we have an Environment module to help our Lambda know if it’s running in a QA, Stage, or Production environment.

For promises, there's a proposal plus implementation with improvements that should be upstreamed soon. JS interop is actually pretty good, if you find the embedding syntax too ugly you can for the most part keep .js files and .res files and they'll work together.

Note that here I'm using the rescript-promise library, which will soon become a part of the core language.

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”.