IME the testers refered to can give very misleading results, they apply a high voltage high frequency field to the outside of the lamp, or to one terminal.
This ionises the gas within and causes it to glow, that only proves that the bulb still contains the correct gas mixture, it does not prove that the filaments are continous or have retained the power to emit electrons.
The easiest way to test flourescent lamps is to insert them into a known working fixture.
The easiest way to test a ballast is to connect it to a known working lamp.
If you suspect that the ballast has a fault that destroys the lamps, then to avoid waste, use well used but proved functional lamps for the test.
A crude test of 2 wire switch-start ballasts is simply to connect them to the line via a fuse, and observe if any current is drawn.
Open circuit=no good
Short circuit=no good
Moderate current=probably OK
That only applies to 2 wire ballasts, those with more connections are best tested with a lamp.
