HOW was the battery tested?
Was it fully charged and then LOAD tested?

Suggest you remove the spark plugs and run the starter with the plug wires away from the spark plug hole. Carb float needle MAY have leaked filling one or more cylinders with gas. IF this is the case, buy and install an inline gas shut off valve and use it when the engine is not running. Also, I have a list of the most common caused of hard cranking in these engine if you would like it, address below, put in proper format and remind me, engine model number and what you want.

Walt Conner
wconner5 at frontier dot com

Same question as Bill above - how did you test the battery? Even a pretty dead battery might give you a reading around 12V under no load - test the voltage across the battery when you're trying to start the engine and see how low it drops.

Have you tried jump starting it off another battery?