Replace Karma (Deprecated) as the JS Test Runner

[gaiety-deque]

Product

axe-core

Product Version

4.9.0

Latest Version

• I have tested the issue with the latest version of the product

Issue Description

Expectation

Test runner operates on a reasonably standard library that is well maintained and documented. Likely mocha, as that is what is used for other tests.

Actual

axe-core test running operates on a deprecated framework called Karma

Karma is deprecated and is not accepting new features or general bug fixes.

How to Reproduce

npm run test:unit or any of it's sibling scripts, a browser appears running karma.

Additional context

This is very likely not a security concern, as far as I can see we never import Karma in such a way to introduce a problem and it's only used to run tests.

[gaiety-deque]

I spent some creative time playing with replacing Karma with straight-up Mocha (reading their "run in the browser" docs), Web Test Runner, and Playwright but kept running into issues. May revisit this another time.