Drop mocha as testing framework

[lnicola]

We currently have a couple of client-side test, using vscode-test and mocha. The latter seems popular, but looking over its dependency tree made me quite uncomfortable.

Let's try to implement simple a replacement for it, if possible.

[Aloso]

I wouldn't recommend writing a testing framework from scratch, that would be reinventing the wheel. There are testing libraries with no (or very few) dependencies, for example QUnit.

[lnicola]

QUnit has no dependencies

I... don't even know what that means.

[Aloso]

@lnicola the devDependencies aren't installed when you use a NPM package, only the dependencies. So QUnit has 3 direct dependencies (5 in total). But QUnit was just an example, there are other options as well.

[flodiebold]

I wouldn't recommend writing a testing framework from scratch, that would be reinventing the wheel.

It's not so much reinventing the wheel, as realizing we don't need a wheel because we're completely stationary 😉