refactor(test): enhance mocha usability

[daiyam]

This PR is:

• adding the command test:dev to be able to run an unique test or set of tests (yarn test:dev -g="Color channels")
• adding the support of Mocha Test Explorer in Visual Studio Code

The dependency source-map-support is used by mocha to reference back to the typescript source file (not the compiled javascript file) when there is an error.

@Tyriar as discussed in #3434

[Tyriar]

Is there a trick to getting this to work? I checked out this branch, ran yarn, installed the extension and see this:

Refreshing loads for a bit and shows the same.

[daiyam]

Here I'm getting:

The updating settings.json is required. Without it, I'm don't get anything.
You might also need to click on the reload arrow.

[Tyriar]

🤷

[daiyam]

Oh! Let's me try in Insiders...

[daiyam]

Yep. I can't get the tests to load on Windows... not sure why.

[daiyam]

Oh! Even test:dev doesn't work on Windows...

[daiyam]

@Tyriar Can you retest the Mocha Explorer? You might need to reload VSCode...

[Tyriar]

Still doesn't seem to work, even after a full clean and re-running yarn/restarting vscode

[daiyam]

Not sure why.. I've tested on Windows with the Insiders version

Do you have any global settings for Mocha Test Explorer or Test Explorer?

[Tyriar]

Doh, had "testExplorer.useNativeTesting": true since it asked that was the issue. Guess it's not ready yet. Seems to be working now

[Tyriar]

Looks good, thanks!