ts-jest VS tsc-esm-fix

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.

Probably because it compiles them to a pre-standard ES5-compatible implementation based on good ol' `Foo.prototype`. And since they've already handled them one way, they can't become spec-compliant without breaking backwards compatibility.

The other place where this shines through particularly egregiously is the support of ESM static import/export. Everybody's build tools been compiling that back down to CJS so hard that Node.js 16+ introduced intentional incompatibilities between CJS and ESM modes just to get people to finally switch to the standards-compliant module system. So you end up in a situation where the library is written in TypeScript with ESM syntax but the only available browser build is a CJS blob which completely defeats the main touted benefit of static imports/exports, namely dead code elimination...

So you decide what the hell, let's switch TSC to ESM and moduleResolution node16, and end up having to use something like https://github.com/antongolub/tsc-esm-fix because the only allowed fix for TSC doing the wrong thing is at the completely wrong level - https://www.typescriptlang.org/docs/handbook/esm-node.html - if you don't see what's wrong with that, you're one of today's lucky 10000...