How to Test Dremel Sliding Switch

Hi all, my Dremel 3000 has stopped working and I assumed that because I was using it to cut small bolts and it was taking a while it had simply overheated or blown a fuse. Fuse in the plug (UK) is fine and nothing looks burnt out inside.

Based on other people's problems I suspect it's the switch that's failed but I'm not sure I'm testing it properly. I've got continuity in some bits but not others but I don't know if that's because it's faulty or because I'm doing it wrong. Can anyone talk me through how to test the switch correctly and what reading I should expect? Should I be getting 0 resistance or is a certain level ok? Just want to make absolutely sure it is the switch before I buy a new one.

Thanks in advance.