fast-check VS intermock

Libraries like JSVerify or Fast-Check offer essential tools to facilitate property-based testing.

Strong agree!

For JavaScript, I suggest folks check out fast-check [0] and this introduction to property-based testing that uses fast-check [1].

This is broadly useful, but one specific place I've found it helpful was to check redux reducers against generated lists of actions to find unchecked edge cases and data assumptions.

[0] https://github.com/dubzzz/fast-check

Brilliant, this is a massive improvement. Previously I was fumbling around in https://github.com/dubzzz/fast-check/tree/main/packages/fast-check/documentation for info.

There's a library for exactly that: FastCheck.

It makes @fast-check/jest, the best option to integrate Jest and fast-check, as it provides an abstraction over both to ease their mutual integration.

The closest that I know of (and I have not used this) is zod-fast-check. It generates fast-check “arbitraries” (test data generators) for property-based testing based on zod schemas. Of course, this requires that you use zod to define your types, which has some downsides. Fortunately there is another tool, ts-to-zod, (which I also have not used) which will codegen zod schemas based on TS type definitions. If you thread these four libraries together you should end up with the ability to write random tests on generated data with very little overhead. In theory.

For something like this, I might break out fast-check for testing. It’s good at generating a wide range of values for a given type, and could help you get good test coverage without having to hand-author a lot of repetitive error inputs.

Yep, I felt the same. I'd been using the builder functions this produces for a while to at least speed up test writing but thought it should be easy to automate so went looking. Turns out there is a tool out there, Intermock, and, while fantastic, it is command line only. Our tool is built on top of that to provide a way to run it in VSCode with a couple of other niceties added.

Whenever I found myself creating another mock object for testing I kept looking at my Typescript types and thinking, can’t something look at that and do it for me? This sent me down a search for a solution and I was so stoked to find intermock which is a command line tool that does just that. While it is still a work in progress and has some limitations I have found it super helpful when writing tests.

I found Intermock a little while ago when I was looking for something similar. It looks relatively inactive, but I didn't even try it out or look into it any further.

My most recent Inception Week has helped me grow significantly as a developer as I worked on an application outside of the browser for the first time in my career. Building on the work of the awesome folks who built intermock, I adapted their tool to be used within the VSCode IDE with the extension Emulative (coming soon to a marketplace near you!). In doing so, I am hoping to do my (very) small part to improve the lives of my fellow developers by building upon the tool chain that so many others have built in order to make the work we do easier and more rewarding.