Dude, test that darn pump already. The fake a lake is an awful test. The water from a garden hose is under pressure. When a boat is on the lake it has to suck water uphill. Any mechanic who would tell you that a fake a lake is a good test is an idiot. No other way about it. Wouldn't you rather know the pump is in fact good or bad so you can stop guessing? It's a hell of alot cheaper to test it than just replace it without knowing.