Update 99_extras.py

tests/99_extras.py

@@ -112,4 +112,9 @@ class A:
 
 bad_dict = {A(): 1, A(): 2, A(): 3, A(): 4}
 assert len(bad_dict) == 4
-bad_dict[A()] = 5   # error
+try:
+    bad_dict[A()] = 5   # error
+    exit(1)
+except RuntimeError as e:
+    assert 'maximum collision reached' in str(e)
+