I am wondering if the wdt will re-start the PIC if prog execution somehow stops
Yes. If program execution stops, and you have the WDT enabled, it will cause a reset. That's what it's for.

There are some exceptions like entering SLEEP, and waking up with the watch-dog timer where it will continue executing code after the sleep instruction, but this is all in the data sheet and easy to lookup.
is there a way to test the wdt ?
No, but some PICs have a register that indicates what caused a device reset.