Step 8: Testing part
You can either reboot to test auto-start or run manually for testing purposes:
You should be able to use buttons next/previous to switch the songs.
Also you should be able to stop song and start again by start/stop buttons.
If the bassplay itself can play modules, please check the functionality of GPIO wiring.
You can test state of pins by /usr/bin/gpin.sh
This scripts returns value of pin defined by the parameter.
You can press particular button ant test whether 1 changes in 0 and vice versa.