You could also perform the test by measuring for a small voltage (like a 1.5v batt) applied in different directions against the diode.
OK reading more carefuly, the FSM doesn't say to isolate each diode but to remove the connections to the stator when using the lamp test. That makes sense, since there is are three possible paths.
Technology has changed substantially since then. Most decent multi-meters come with a built in diode tester these days.
The special tool was read like this, which helped identify bad ones without initially isolating.
approx 1.75 amps across each is good
low on two and 0 amps on one is diode shorted.
normal on two, 1 amp on one is diode open.
