test ref with exception in the callback
Unhandled exception in weakref callback:
Traceback (most recent call last):
  File "\.\+weakref_callback_exception.py", line 21, in callback
ValueError: ('weakref callback', (<ref>,))
collect done
test finalize with exception in the callback
Unhandled exception in weakref callback:
Traceback (most recent call last):
  File "\.\+weakref_callback_exception.py", line 21, in callback
ValueError: ('weakref callback', ())
collect done