Since you mentioned two switches, I assume your light is a two way light. Here is a diagram of a two way setup.
As Dale and Bill had mentioned, there are many reasons for you to get a false indication of power to the lamp at all times. Without knowing what was used as a "wire tester" and the skill of the operator, it is hard to comment on.
One other reason to get an indication of power all the time is that the line (hot) wire could be connected to the light and the switching done on the neutral side. I have seen this in some older houses.
Since the most common cause of the problem is a switch, I would test them first with an ohmmeter being sure to kill the power to the circuit first. Check that each switch is capable of opening (high resistance) and closing (less than 1 ohm) the connection between the common to A and common to B terminals of the switch.
One other possibility if the light has never worked since you got the property... the previous owner may have tried to replace a switch and wired it incorrectly. Use the above diagram to see how it should be wired.