Simple. You need a voltmeter.
Test #1: Does it click? If yes, go to test #2 If no, go to test #3
Test #2: Test voltage at two large studs on solenoid. Should show battery voltage on both. If it does, solenoid is working and you should be looking elsewhere. If not, check battery and cable connections. And starter.
Test #3 Check voltage at two small studs on solenoid. When attempting to start, should show battery voltage on one stud and zero on other one. If no voltage on either , check start switch, fuse, and wiring. Also neutral start switch if it happens to have one. If battery voltage on both, safety switch is not activated or is defective, or ground wire is defective or missing if it has no safety switch.