Add end2end tests

[camillobruni]

• Move unitests to run-unittests.mjs
• Move common test driver and server setup to separate helper.mjs module
• Add SpeedometerReady and SpeedometerDone events for easier testing
• Add simple end2end tests

[flashdesignory]

LGTM

[julienw]

thanks, this looks good to me
I only have a few nits before landing :) see comments below
thanks for the new tests!

[camillobruni]

Updated a few more things

• updated required selenium version to 4.27 to fix local runs
• installed better error handlers to catch runner errors in the end2end tests
• moved benchmark-runner-tests.mjs to tests/unittests

[julienw]

Thanks, I like the fact we call a function better (didn't want to highlight it before :-) )

BTW I wonder if there's a way to run the tests headless too. How does it work on CI, is there a X server or something?

[camillobruni]

headless would mostly depend on how the browser is set up.
I know how to run chrome headless e.g. it basically only needs the --headless command line flag, I think firefox has the same flag, no? (We can add that by default or make it customizable in an additional PR?)

Given that we currently only run on macOs it wont matter for the official testing (there is no real headless on macOS I think).