Unit test failed when component has svelte-multiselect

Hi @janosh, I like to thank you for creating such a great component! I love it!

Everything works great so far (v4.0.0) in my svelte app until I tried to add some unit tests. Test failed when I tested component which has svelte-multiselect, Jest threw error (Vitest broke right away) like this:

I’d already setup transformers so it’s not a ESM problem in Jest, and other tests passed with different svelte libraries.

Here is a reproducible repo that you can check: https://github.com/davipon/test-failed I simply import svelte-tiny-virtual-list & svelte-multiselect in the same test file and try to render them. Test would fail before rendering Multiselect:

test('render multiselect', () => {
  render(Multiselect, { options: webFrameworks });
});

I’m not familiar with creating Svelte package, but I found a difference in these two libraries’ index.js: svelte-tiny-virtual-list:

svelte-multiselect:

Not sure if information above can help, and thanks again for your hard work!

[davipon]

I also tried transformmode but it failed as well.

Anyway, I asked in Vitest Discord channel and got the answer! We need to use dep.inline in Vitest:

test: {
  globals: true,
  environment: 'happy-dom',
  deps: {
    inline: [/svelte-multiselect/]
  }
}

Now we know how to deal with transpiling errors when unit testing most of the Svelte component packages (I believe) in both Jest and Vitest, I’ll create a PR to add a Unit Test section in README with examples.

Thanks again @janosh, your comments really helped me to dig in and find the root cause, please kindly close this issue, have a good one!

[janosh]

While test still failed in Vitest, I couldn’t find the corresponding config in Vitest so far, will raise a ticket there.

Thanks. Could you link this issue over there? I’d like to subscribe to your vitest issue.

this seems to be a general problem for future Svelte ecosystem when it comes to unit testing.

Indeed which is why I’m very curious to hear if there’s a recommended solution.

I can create a PR for that if you think it’s OK.

Sure that would be great!