A common failure mode for coils is insulation breakdown in the secondary winding. This results in little or no spark, but no real change in resistance. A very high resistance reading can tell you that a coil has burned out, but a normal one doesn't tell you that it is OK. I don't know of a worthwhile way to check capacitors other than on a tester or by substituting a known good one. If there is no spark and you have checked the obvious things (kill switch contact has become grounded, broken or disconnected wires, bad spark plug), my solution has been to take the ignition unit to someone who has a proper tester - usually the friendly local mower man. Of course proper enthusiasts always seem to have spare ignition units, which is a quicker and cheaper way to see if that is the problem.