Many of your favourite desktop mach test commands now work with Firefox for Android.
These commands now explicitly support Firefox for Android, running tests against a connected Android device or emulator when run from a Firefox for Android build environment:
mach robocop mach mochitest mach reftest mach crashtest mach jstestbrowser mach xpcshell-test mach cppunittest
Note that most commands allow running the entire suite (rarely a good idea!), a directory or manifest, or a single test.
As usual, detailed information on testing Firefox for Android can be found at https://wiki.mozilla.org/Mobile/Fennec/Android/Testing.