Tests present errors about types, inconsistently

[clark-lindsay]

Hey! To preface my issue, I am new to Svelte, and so this is my first time jumping through most of these hoops.

Following the Svelte guide for setting up a TypeScript project, I built myself a script to set up a minimal project with a single test for the "Hello World" App component that the default template comes with. I followed the testing setup guide from testing-library, which is what brought me here.

I can run the script to build a new project, cd into it, and run the test with yarn jest, and it passes. If I then edit the test file in any way, say adding an extra 'expect(5).toEqual(5);`, then the tests blow up at me and tell me that they "cannot find name 'test'" and ask me if I forgot to install type definitions.

If I remove the "offending" change, the issue persists. If I also delete the node_modules folder and run yarn install again, then the test will pass.

Here is a repository with an app fresh off the presses from the script, which I was just able to reproduce the issue with on my system (macOS 10.15.5).

I would hugely appreciate any help that you are able to give. Please let me know if you need any more information!

[DennisSkoko]

I'm a bit late but maybe it can help someone else who is struggling on this like me. I had the same issue (except that the errors for me were consistent) and tried following the steps TypeScript was writing, adding jest to types. However after adding it, I had another error regarding svelte and saw that the base tsconfig (the one that is extended from @tsconfig/svelte/tsconfig.json) had svelte to the types array, so I needed to specify both jest and svelte, like this:

{
  "extends": "@tsconfig/svelte/tsconfig.json",
  "compilerOptions": {
    "types": ["jest", "svelte"]
  },

  "include": ["src/**/*"],
  "exclude": ["node_modules/*", "__sapper__/*", "public/*"]
}

After looking at your tsconfig.json and saw that you didn't specify the types option. I would recommend trying adding this and see if this helps. I can't really explain the inconsistent errors but hopefully the errors will be consistently gone for you after adding this option.