Oil Warning Light intermittent - Pump Replacement?

[Gtiracer]

Recently my oil warning light has decided to come intermittently on and off when I'm driving, it will come on for about 2 seconds then flash off again. I took the car out and it did it twice on one short journey so I'm guessing it means duff sensor or pump (obviously I have checked the actual oil level which is fine)


My question is how easy is it to replace an oil pump if this is what needs doing and how can i test my oil pressure?