#17779: test_osx_env now works with unittest test discovery.  Patch by Zachary Ware.
#17789: test_random now works with unittest test discovery.  Patch by Zachary Ware.
#17790: test_set now works with unittest test discovery.  Patch by Zachary Ware.
Fix indentation.
Minor typo in example.
#17413: make sure settrace funcs get passed exception instances for 'value'.

Patch by Ingrid Cheung and Brendan McLoughlin.