I would plug something in top, then bottom of receptacle to verify with a load(or Wiggy)you have voltage.
Its like Water heaters, instead of removing wires from Element for testing, use an Amprobe and a Voltmeter, If you have voltage to Element and NO load, the Element IS open.
More work to open and measure resistance.

Back in the 70's the big thing was splitting the tab on the recept so that the top outlet was controlled by a switch for plugging in floor lamps and the bottom outlet was constant hot. Back then a lot of houses did not have ceiling lights. Most recepts were wired with a black/red/white wire with one color going to a switch. Maybe this will help to determine your situation

Like jerro was mentioning the red sometimes will be the switch leg, if they are separate to the panel, this may not be the case.
Switching half a receptacle is still done, sometimes on a 3 way, with other switch near the bed?