When my ramshackle, made-from-junk arcade joystick had some trouble on my Mac, the OS didn't have much to help—I couldn't even find a relevant System Preferences panel, let alone anything useful for troubleshooting. Searching for an app I instead chanced across Gamepad Tester, a website that detects whatever you have plugged in and offers useful feedback. There's even an API for developers.
When connected, this tool displays the current state of your gamepads, inputs, joysticks, and anything else that can be reported by the HTML5 Gamepad Api.
This is also useful for debugging broken controllers, experimental hardware, and more.
Did the trick! Turns out my joystick is broke.