can anyone tell me if there's a way to test the alternator in my L reg disco.When driving the battery light flashes on and off someone tod me it could be the battery but wanna test the alternator before i go and get a new one

i'd borrow a know good battery and put that on. then connect a multimeter across the battery terminals. it should read 14 to 14.5 volts when the engine is running. if it's less than that then yer altenators fooked. if it reads OK then it's yer battery.