Moving to Vitest with help of jsdom

[patricknelson]

Since Snowpack is no longer active, moving to modern Vitest and fully JS based dom (jsdom) which is very fast and works very well across various environments.

Change log:

• Converted both the non-shadow-DOM and shadow-DOM based tests over to using Vitest (https://vitest.dev/).
• Using typical component nomenclature in test (i.e. TestTag) and ensuring unit test file matches tag name. Should be useful if we add more tests later with different components.
• Similar to Fix for #12: Ensure original named slot tags are retained when not using shadow root. #13: Adding .editorconfig and .gitattributes to enforce the repo's existing formatting style (i.e. 2 space indentation) and since I'm on Windows, combatting the committing of crlf chars at the end of each line 🤦‍♂️
• Similar to Fix for #12: Ensure original named slot tags are retained when not using shadow root. #13: Adding .gitignore to prevent committing of my IDE files (Jetbrains in my case).

[patricknelson]

p.s. If you merge this first, I'll update my PR #13

[patricknelson]

Necessary since files are named .js and not .mjs. Tested this locally using npm link and it doesn't appear to affect imports of the project itself (i.e. import Component from "svelte-tag").

[crisward]

I didn't realise JSDOM supported web components. I've had a quite a few client tests fail in the past due to unsupported api's so tend to go the browser route. However in this instance JSDOM / Vitest appear to work well.

Thanks for the work on this.

[patricknelson]

I was worried about that too. I just gave it a shot since the API was so similar. I’m really happy the transition was relatively easy and painless.

Since my PR #13 was already merged, I’ll have to resubmit a new PR that does the same thing but addresses the failing tests since of course the whole unit test abstraction was rewritten/recreated. This of course meant the unit tests from the other PR weren’t carried over and started failing (there would have been conflicts anyway with the introduction of the <!--<TestTag>--> comments by the compiler).

More to come soon.