tinyspy VS uvu-expect

You may have heard of vite, the slim fast dev server that scored an amazing as deserved 98% satisfaction on the state of js survey 2021. It's creators found unit testing too cumbersome and slow and decided to add their own perspective to the task. The result is vitest: it runs a vite server under the hood to transform the code to test as fast as possible, uses an enhanced flavor of chai to have jest-compatible assertions, integrates DOM mocking using jsdom or happy-dom and even the tiny-spy library that was just built as a separate library to allow for easy reuse is small and compatible with jest.

Assertions on mock functions (compatible with sinonjs and tinyspy).

This setup works really good! But there’s some minor details: The assertion errors thrown by Chai are slightly different than those expected by uvu., so sometimes I’d get messages or extra details that are not so relevant to the test itself. Another issue is that I’d receive diffs comparing undefined to undefined when an assertion failed. As a proper developer with too much free time, I went ahead and decided to experiment with writing my own assertion library built on top of uvu’s assertions that I called uvu-expect. Here’s more or less how I did it.