Interesting... I guess it's meant to bypass the timer to power up individual components. The Robinair brand brought Frigidaire to mind, but I think they made tools for other appliance manufacturers, too.
This is for testing the main motor on WP reversible DW motors, it would work on WP built DWs from the mid 60s till the tall tub models that came around about 2000.
It was a neat little tester that has very little usefulness as it is very easy to test a motor with an ohm meter and just a physical examination.