What points of contact would your hands need to get in this situation to get hurt? In this case do we suspect hot/ground or neutral/ground to be switched? Which one can the tester identify and is that the dangerous one?
We suspect that there was a hot ground in this situation. You could be electrocuted if you touched the chassis of the equipment plugged into this outlet or anything else it touches, and a real ground like a water pipe or other metal structure. You might even draw some current standing on a concrete floor if it's a bit damp and your shoes aren't good insulators.
Hot and ground may have been swapped (in which case the equipment would not be able to power up), but it's possible that the "ground" was hot for some other reason. The simple 3-light tester should show this condition. If all three wires were hot, it would not show a fault (except that it would indicate the outlet was "dead").
A swapped ground and neutral is not unsafe by itself (as long as all the connections are good), but it will inject an incredible amount of hum into a system (ask me how I know
), or at least it will with non-pin 1 compliant equipment. The tester cannot detect this condition, and it would be difficult without internal inspection of the wiring.
A hot ground, especially on installed wiring, should be very rare, but one way it has happened is with isolated ground outlets, often used for computer or other technical equipment. Until recently, BX cable (flexible armour) was not available with a green wire for the isolated ground, so electricians used 3-wire cable, and used the red wire (appropriately taped) as the isolated ground. The bare copper wire stayed as the regular ground for the box.
That works OK, as long as all the rules are followed. On one installation, apparently one guy worked on one end, and another did the breaker panel. The second guy though hooked it up like any normal split outlet, to a double breaker. Once the breaker was turned on, there was 120V on the ground pins of that outlet. The computer that was plugged into it worked fine, and no one even got a shock because it had a plastic case. It even worked with an ethernet connection because the LAN CMMR was good enough for 120 VAC. But when they switched to one of those old 50Ω coax LANs. Once that was hooked up, the sparks flew!
One other wiring fault that gets mentioned from time to time is a swapped hot and neutral. This is probably far more common than anyone realizes, because under most conditions and with most equipment, it's not a problem. It's not much different than "balanced" power, which has 60 VAC on the hot, and 60 VAC (opposite polarity) on the "neutral". The simple tester will show that as a fault.