Needed for {T190710}. The initial idea was to run both core and extension/skin tests from core, using either mocha or cucumber (or possibly both). I do not think that is a good idea any more. Looks like the way forward is to run tests for each repository (core, extension, skin) from the repository.
# TODO
# Done
馃彎 [[ https://gerrit.wikimedia.org/r/c/mediawiki/core/+/429018 | 429018 ]] selenium: Abstract test command behind 'npm run'
馃彎 [[ https://gerrit.wikimedia.org/r/c/integration/quibble/+/428040 | 428040 ]] Run `npm run selenium-test` instead of `grunt webdriver:test`
馃彎 [[ https://gerrit.wikimedia.org/r/c/mediawiki/core/+/428344 | 428344 ]] selenium: Abstract test command behind 'npm run'
馃彎 [[ https://gerrit.wikimedia.org/r/c/mediawiki/core/+/428373 | 428373 ]] selenium: Abstract test command behind 'npm run'
馃彎 [[ https://gerrit.wikimedia.org/r/c/mediawiki/core/+/428374 | 428374 ]] selenium: Abstract test command behind 'npm run'