Any good voltage tester or volt meter will do, as long as it is fairly accurate and can read 300 volts.
A 230 volt outlet in a residence most commonly will have three holes. One will be radically different from the other two and will be the ground. The other two will read 220 volts between them and 115 volts to ground.
The outlet size and configuration will depend on the load you are putting on it and the duty, ie you can get a light residential type outlet all the way to pin and sleeve types for industrial use.
Note that you don't necessarily need an outlet as many things can be direct wired and direct wiring is desirable with motor loads on equipment that remains stationary like air compressors and welders at a work station.