Ballasts are difficult if not impossible to test directly. If you have an identical ballast to use as a reference, you could use resistance tests to check for shorted or open windings, but that's about it. And with electronic ballasts, there really aren't any "windings" to check. Often, a bad ballast will buzz or overheat, but not always.
Basically, if the ballast has input power, and the lamps, lampholders, and starter (if any) are OK, process of elimination leaves a defective ballast.
