Can I intercept "instance variable XYZ not initialized"

I’m working with Test::Unit and want to reduce the amount of noise in
the results. One annoying problem with negative test cases is “warning:
instance variable XYZ not initialized”

I may simply be doing things wrong but it seems that throw-catch and
begin-rescue aren’t capable of ‘catching’ this message.

I’d rather avoid post-processing the output. First because it decouples
and duplicates the references. Secondly because I don’t want to mask
legitimate errors.