Convert some old-style string exceptions to class exceptions.
diff --git a/Lib/test/test_unpack.py b/Lib/test/test_unpack.py
index 1bfd478..25324c0 100644
--- a/Lib/test/test_unpack.py
+++ b/Lib/test/test_unpack.py
@@ -100,7 +100,8 @@
 
 # unpacking a sequence where the test for too long raises a different
 # kind of error
-BozoError = 'BozoError'
+class BozoError(Exception):
+    pass
 
 class BadSeq:
     def __getitem__(self, i):