- Put on the gear to test
- Turn on the shower (adjust temperature to your liking)
- Walk into the shower
- Perform a series of movements (walk in place, jumping jacks, etc)
- Turn off shower
- Inspect gear for damp spots on the inside
This method allows you to control energy exertion (minimize sweat) and exposure time while at the same time simulating "real" conditions.
Boots might do fine if you sit them in a bucket of water, but once you start walking (bending that fabric and getting things moving) you might find there are leaks.
As for determining whether
this softshell will keep you dry in a rain storm for about X hours
The surest way to find out is put in on and go hike in a rainstorm for X hours. Carry a spare in case it fails.