Could I try and place a pot or two in the freezer? I would first fill it
with bonsai soil and water it allow it to drain well then freeze it.

I don't think that would be an accurate test. You want to see how the pot will
respond to alternate freezing and thawing and fluctuating moisture levels. If
you want a realistic test you will need to bury one or two pots in the ground
and leave some outside all winter in various locations. The weakest part may be
the glaze rather than the pot itself.
Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)