[Svelte] Tests not recognizing the typescript in .svelte files

[DiogoVCS]

Created a stackoverflow question regarding this issue here, with more code snippets.
Clean project, using the nx empty workspace (or with an angular one, its the same), added a svelte project using the command line nx g @nxext/svelte:app my-app, then added a component using nx g @nxext/svelte:c my-comp and after inserting this line in the MyComponent.svelte file:

let name: string;

the tests stop working, giving the following error:

 FAIL   my-app  apps/my-app/src/components/my-comp/my-comp.spec.ts
  ● Test suite failed to run

    ParseError: Unexpected token

      at error (../../node_modules/svelte/src/compiler/utils/error.ts:25:16)
      at Parser$1.error (../../node_modules/svelte/src/compiler/parse/index.ts:100:3)
      at Parser$1.acorn_error (../../node_modules/svelte/src/compiler/parse/index.ts:93:8)
      at Object.read_script [as read] (../../node_modules/svelte/src/compiler/parse/read/script.ts:51:10)
      at tag (../../node_modules/svelte/src/compiler/parse/state/tag.ts:205:27)
      at new Parser$1 (../../node_modules/svelte/src/compiler/parse/index.ts:52:12)
      at parse (../../node_modules/svelte/src/compiler/parse/index.ts:216:17)
      at Object.compile (../../node_modules/svelte/src/compiler/compile/index.ts:91:14)
      at Object.process (../../node_modules/svelte-jester/src/transformer.js:21:25)
      at ScriptTransformer.transformSource (../../node_modules/@jest/transform/build/ScriptTransformer.js:464:35)

if I insert instead just:

let name;

it works again.

Unfortunately the TypeScript usage is a dealbreaker for us.

[DominikPieper]

Hi,
thanks for your issue. I added some changes which will come with the next release and simplify this. For now for you to add for the tests:
For the jest.config.js change the svelte transformer to this (with a path in your application directory)

'^.+\\.svelte$': ['svelte-jester', {
  'preprocess': 'apps/<project>/svelte.config.js'
}

and add a svelte.config.js in the dir with the following.

const sveltePreprocess = require('svelte-preprocess');

module.exports = {
	// Consult https://github.com/sveltejs/svelte-preprocess
	// for more information about preprocessors
	preprocess: sveltePreprocess()
};

I'll add the files and paths as a default in the next release and add a option for the build to read in the config file as well to simplify the custom configs