The current unit testing setup has some issues:

• depends for setting up and running a mediawiki server just to execute JS unit tests. this can prevent JS devs from contributing and hinders onboarding because it requires knowledge about multiple ecosystems and mediawiki-specific skills
• depends on a browser as execution environment. test execution requires switching to browser, manual reloading. also slow test execution. this is an impediment for TDD.
• test dependencies are hidden outside the test via resource loader, making them hard to understand and - again - couples js tests to mediawiki and reduces cohesion of the system. Doing it this we reduces decouling, but also decreases cohesion of the system
• lack of IDE integration making executing, debugging, interpreting results, etc. unneccessary hard

Implementation: There are options to execute qunit tests from CLI and tools, but
enabling this requires setting up a browser environemnt using e.g. jsdom. See if this is feasible, otherwise port Lexeme tests to jasmine or others.

Scope: As a proof of concept, integrate it and port one tests. Finish porting
the others with regular work (whenever we need to touch the test anyway), or
find/create a codemod script to automate.