ts-jest VS jest

Argument of type X is not assignable to parameter of type 'never' #2610

First, you can't use jest right out of the box, becuase Jest does not support ECMA script nor Typescript. For that, you need to use another dependency like ts-jest, which is a wrapper of jest itself. And maybe even a Babel preset if I need it to work with Babel.. Let's see what we have to do to get this to work.

use ts-jest and set up Paths Re-Map

Jest's out of the box config for TS doesn't do any type checking. You can integrate https://kulshekhar.github.io/ts-jest/ or you can call ‘tsc’ yourself separately

ts-jest has had some strange performance issues and workarounds in the past, though I haven’t used it very recently so it might have fixed those by now.

Since we're working with TypeScript, we can use ts-jest, which conveniently brings Jest along for the ride:

I want to save you from manually copying the snippets one by one, so here is a Gist with the complete test file. This can be easily executed with Jest (or ts-jest for TypeScript).

See the Jest configuration docs to learn more about Jest configuration. ts-jest also has good documentation.

Using @swc/jest to compile code to CommonJS is much faster than babel-jest, ts-jest which have long cold starts when executing tests in a large project.

What's even more amazing is look at the source code: https://github.com/swc-project/jest/blob/master/index.ts

swc is blazingly fast, try it: https://github.com/swc-project/jest