I would also get a meter on it just to triple check. Here's what I send to my RV groups on how to measure a standard 120-volt outlet.
While I have abandoned my outlet tester I explain why simple AC voltage measurements can be tricked. The rare but hazardous RPBG will measure exactly the same as a properly wired outlet using a simple AC meter.
http://www.johnhroberts.com/OD1.htm The less hazardous, but still incorrect line-neutral reverse can be effectively metered with a simple AC meter since ground to neutral will not measure 0V.
I have shared this before a crude but simple way to identify if outlet pins are energized is to use a cheap Neon lamp probe.
Holding one lead of the neon lamp probe in your bare hand, touch the other lead to the outlet pins. Any hot pins will cause the neon lamp to glow dimly. Current "should" be limited to well below dangerous levels, but don't do this while standing in your bathtub full of water.
I do a similar trick with a VOM but am reluctant to share details since you can get shocked using the wrong mode.
JR