The test using class initarg failed, because it was lacking a

__safe_for_unpickling__ attribute.

Lib/test/pickletester.py

@@ -14,6 +14,9 @@ class myint(int):
         self.str = str(x)
 
 class initarg(C):
+
+    __safe_for_unpickling__ = 1
+
     def __init__(self, a, b):
         self.a = a
         self.b = b