There is a tester for GFCI breakers. Any electrcial company would have one. The cost to have it tested is probably about the same (or more) as just installing a new breaker yourself. If you are capable of changing a breaker I would suggest you do that first. If the problem dosn't go away then call the elelctrican. I would also speculate that the problem (if it isn't the breaker itself) is in the pump motor not the wiring.
Two short, relevant stories:
I had a GFCI breaker for my master bath Garden Tub/Spa that I never tested in five years. I only used the Tub a couple of times a year - if that much. One day my elelctrican friend reminded me that I should test the breaker annually. When I hit the test button the breaker tripped and would not reset. I ended up repalcing the breaker (about $45 bucks). The point is that these things do fail even when not used much.

I also had an outdoor driveway latern/light installed at the entrance to my driveway about 200 feet from the garage. My elelctrcian installed a GFCI outlet at the latern rather than in the garage where the power feeds from because he said a long wire run tends to cause the GFCI to trip whereas having the GFCI close the point of load still protects the device but is less prone to nuiscence trips.
Good luck, Mike