This can be accessed when you have already entered the Motor Test Mode by depressing the DISPLAY/SCROLL key again at any time in the Motor Test Mode.
Access Motor Test Mode: Hold down the DISPLAY/SCROLL key while turning the power switch "on." You will then see the test appear on the display, release the DISPLAY/SCROLL key.
All the LEDs will light up until you have depressed another key. To test the key's responses simply depress each key and see that it responds with its proper function.