You just did.
You can test the power vs. the published guide number by using manual mode (manual on flash and camera) and shooting something at the correct measured distance (distance=GN/aperture) and see if it's properly exposed. Keep in mind that each zoom setting has its own guide number.
Attach a midrange zoom lens like a 24-70, zoom it to various focal lengths with the flash pointed straight ahead and half-press the shutter to see if the autozoom works.
You can test fire it at full power and time the recycle time if you want.
Go into a dark room with a blank wall, select one shot AF, then select various focus points and see if the AF assist light illuminates and allows the camera to lock focus. The AF assist shoud allow the camera to focus pretty quickly on a blank wall in the dark.