Honestly, to me, the 'machine gun sound' sounds like dead battery. It sounds like the starter is trying but doesn't have the juice to turn it over.
Now, I know you said you had the battery on a tester, but putting out 12.5v on no load does not always equal 12.5v under full load. It could be the battery is dropping voltage when you put an amp draw on it, and it just doesn't have the juice.
If you're pressing the starter button and getting 'something' that's tied to the button, then your kickstand switch/neutral switch/kill switch/clutch switch are working properly, AFAIK.
Never ride faster than you can stop