ts-jest VS svelte-jester

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.

ts-jest: A transformer for handling TypeScript files.

Anyway, I ran into this exact error this morning setting up Jest for a TS script. I fixed it by just following the getting started instructions for Jest as well as ts-jest.

svelte-jester: precompiles Svelte components before tests.

I’m using jest with svelte-jester and @testing-library/svelte.

While I mentioned in the beginning of the article that I am relatively happy with the current state of my reference TypeScript monorepo template, I still think there are a couple of things that can be improved. Chiefly I think that Yarn 2 (‘Berry’) is still not as mature as I would like it to be. Support for ESM for instance would be awesome, the lack of which caused me some problems in trying to make Svelte work within the monorepo. However, I think it is very worthwhile what the Yarn team attempts to achieve with Yarn 2 and I am happy to support it by trying to make it work in the monorepo template.

I need to test some components that require svelte-spa-router by using jest. Well the problem is, an import from svelte-spa-router causes the error on my previous successful tests. Came across this kind of issue on github https://github.com/mihar-22/svelte-jester/issues/7 and try to replicate the solution like this.