How to test starter solenoid...

[5 Alive]

Out on the water yesterday and turn the key and nothing. After checking the usual, in gear, kill switch ect... I play with the key and finally get some response. Run back to the ramp to see what's going on. Shut the engine off wait a second then turn the key and nothing. (glad I got back to the ramp at this point!) After some more fiddling it starts up. The last three key turns have all cranked the engine but now I'm worried when it will act up again. I'm guessing it's the starter solenoid but how do I diagnose the problem if it's gone?

[Michiganfishing]

Take a screw driver or something to cross the main terminal posts. Before doing that I’d check by tapping on the outside lightly, they tend to stick