Is there a way to test achievements without actually getting them in the game? like running a test to see if the achievements actually register.
No. They have to be in the game and in dev console for them to work.
And yes, you ONLY have to change the App Version Code each time you upload an update to your APK, add only 1 to current version code.
And save the current number each time, trust me!. I updated my APK maybe 5 times in one day, and i had to redo it twice cause i forgot what version code I was on.
Also, in the app version, i would do something like 126.96.36.199, 188.8.131.52, etc, etc. Cause when you update, it will show a list of your apk's, and when it's in alpha testing you can tell your testers what version they should have.