To test an amplifier, you need a known good signal source at a level that's appropriate for the input of the amplifier. You also need a means of testing/comparing the signal levels in and out of the amplifier.
For the hobbyist/consumer, an installed antenna known to produce reliable signal reception and a tuner with good metering functions is the only cost effective tools likely to be available. (Obviously, lab grade test gear is far too expensive.)
I have been able to accomplish a fair amount of testing and tuning of antenna systems using the metering capabilities of my SiliconDust HDHR type tuners.
http://forum.tvfool.com/showthread.php?t=820
If your TV has some signal metering functionality, and you perform the non-amplified test of each antenna, you'll have the signal source and metering to perform a test of the preamp.
Be very certain that you don't also have some other connection or component failure. This is why I suggest you start at the antenna, make sure it works and is aimed well, then add the next parts of your system. When too many parts are put together at once, multiple failures can be extremely difficult to isolate and resolve.