My hot air soldering skills are very much in the “novice” category, so I make sure to test each joystick breakout board before final soldering and mounting in the case. (Learned from hard experience.)
The re-used breakout I’m using is single row, .10″ on center, which happens to be the exact spacing of DB9/15/25 connectors. So, I stuck some pogo pins into a DB15 (because, why not — DB9 is fine), soldered the connector, and hooked it up to my test bed (which just runs the same joystick software with debug mode on).
I attach the “joycon” stick, hold the pogo pins to the board, open serial view, and move the stick around. If the values look good, I know it’s safe to proceed.