You can test a ballast using a True RMS DMM,test for Open Cicuit Voltage across the socket, and for Short Circuit Currrent across the socket. SCC can be tested with a meter with a "feed through" feature,(my Fluke 179 has 10 amp capability and is protected by a fast acting fuse),or I saw at a trade show a screw in device with a shorting loop attached to it for use with a clamp around type meter.
If the ballast has an ignitor, the X3 lead needs to be disconnected before testing to prevent meter damage. I found specifications for a capacitor that can be placed across the meter leads to avoid disconnecting X3, but I can't read the rating on mine anymore, and I don't remember which manufacturer I got that from(sorry).
Sometimes the ballasts have the SCC,& OCV marked on them, if not Advance Ballast has a "Pocket Guide To H.I.D. Ballasts" available that lists them.
If OCV and SCC are correct and the ballast uses an ignitor and it still doesn't work,the ignitor is usually the problem.
My concern with the screw in testers is how do they indicate a good ballast? How does it know the difference between say a good 175 watt M.H., and a 400 watt M.H. with a weak capacitor? Similar OCV, But different SCC.
Hope this helps