Ignition coil bench test?

BillGrissom said

You don't need the ballast resistor if only charging up the coil for an occasional spark test...

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There are a few good reasons to use a ballast. The ballast will limit the coil current, so the coil test is realistic for normal condition. Without the ballast the coil current can be much higher, and coil energy increases by square of current increase. The ballast originated when 12V replaced 6V, the ballast typically has a value close to coil resistance. Without the ballast, coIL current would be double, with energy 4x. With energy 4x, yeah there may be spark for a sick coil, and perhaps not with ballast.
The next reason, to test in a safe way and not destruct the coil under test. Example is testing a low Ohms (0.4) e-core coil. At 12V, the coil current could reach 30A, being inductive load, not many spare parts bins have a switch to clear that! The 360W of dissipation in the plastic potted coil, will likely char the enamel winding insulation of the primary coil. Also the human shock hazzard of death, in the intervetion as wires are smoking on the bench.