Issue 6717 - Part 2: run qunit in headless firefox

package.json

 {
   "name": "adblockpluschrome",
   "repository": "https://hg.adblockplus.org/adblockpluschrome",
   "license": "GPL-3.0",
   "dependencies": {},
   "devDependencies": {
     "//": [
       "'dmg', 'extract-zip' and 'ncp' are needed by the module",
       "adblockpluscore/test/download_firefox.js."
     ],
     "dmg": "^0.1.0",
     "eslint": "^5.1.0",
     "eslint-config-eyeo": "^2.1.0",
     "extract-zip": "^1.6.5",
     "geckodriver": "^1.9.0",
     "ncp": "^2.0.0",
     "nodeunit": "^0.9.1",
     "selenium-webdriver": "^3.6.0"
   },
   "scripts": {
     "lint": "eslint *.js lib/ qunit/ ext/ test/",
-    "run_tests": "nodeunit test/*",
-    "test": "_run () { python build.py devenv -t $1; npm run run_tests ; } ; _run",

[Sebastian Noack, 2018/08/23 16:38:44]

I'm wondering why do we need to define a sheel script function just to call it
right after? Why can't we inline it?

Also why make the target for build.py configurable? The tests will run on
Firefox regardless. So passing in anything other than "gecko" seems pointless.

[tlucas, 2018/08/23 18:56:02]

Making it configurable was the reason to do this, yes - the argument ("gecko" in
our case) would have been passed in some weird way to "npm run run_tests"
instead.

For "why configurable" -> we might consider this premature optimization, but
already given that Edge (and likely Chrome too) will be build on a different
machine (and in parallel), this is meant to "build" and "test" for whatever
platform is handled by the current CI - job. Then again, this strongly supports
adding an abstract test_runner.js right from the start.

Please tell me what you think.

[Sebastian Noack, 2018/08/23 21:54:20]

It seems we have to touch the CI configuration again anyway, once support for
other browsers have been added, since if the CI (or yourself) would already try
to run "npm test -- chrome" it will potentially explode, since with the current
implementation this would essentially run a build for Chrome on Firefox. So IMO
we could as well just hard-code gecko here for the time being, making sure that
always the correct devenv is built for the only browser supported so far.

[tlucas, 2018/08/24 10:25:08]

Done.

+    "pretest": "python build.py devenv -t gecko",
+    "test": "nodeunit test/*",
     "posttest": "npm run lint"
   }
 }