I think you could do it with a pulse generator, but I haven't tried it. You would need to know the characteristics of the signal at certain speeds though so you could generate the signal. Or you could run a wire from another car that has a working tach.
The best way to determine if your tach is broken is to connect one lead of a light bulb to the signal wire from the distributor and the other light bulb lead would go to ground. Start the engine and increase the RPM's. The bulb should dim. If it does, you've got a proper signal and the tach is bad.
The other way is to connect a hand held tach to the distributor signal wire and see if that works. If it does, you've got a bad tach. We used to use the combination Dwell/Tach meters to adjust the points on the old type distributors. I happen to still have mine....it comes in handy. I know they really don't make this meters anymore, but someone you know might have one collecting dust in their garage.