For spark - pull off both of the plug wires , use the plug and hold it against a clean ground/ or the motor and crank the motor over( so it doesnt start on you) - you should see a bright blue spark when it fires ( and or a shock) .
To see if the pistons are moving- while the plugs are out - use a small screwdriver and poke it into the combustion chamber and touch the piston , hand cycle the motor over- and you should see the screw driver move back and forth- if it doesnt, then the rod is broke.
Twin cylenders will run with one broken rod.