I don't live in a freezing climate, so I never test the freeze / boil protection. On my truck I flush it enough to where it really isn't necessary. However it takes the older, inexpensive green Prestone concentrate.
I have never used test strips. Perhaps I'll try them. They certainly can't hurt. I now have 5 gallons of concentrate for my Jeep, along with 5 gallons of 50/50 premix for my Toyota. So I'll just do as I mentioned. Suck and remove, then refill and drive.
After several "suck & fills", I'm sure the condition of the coolant will be good enough so it will no longer be a concern. On my truck, I'll just keep draining and flushing it like I have been all these years.
It's easy to do because everything is easy to get at. I can even disconnect the overflow tank, drain and flush it with a garden hose while everything else is draining.