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Since Snowpack is no longer active, moving to modern Vitest and fully JS based dom (jsdom) which is very fast and works very well across various environments.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

[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.