Fix the sizeof test for dicts with shared keys. (#4311)

By accident the size of the empty dict keys object matched the
size of values array.

Lib/test/test_sys.py

@@ -1074,6 +1074,7 @@ class SizeofTest(unittest.TestCase):
             fmt += '3n2P'
         s = vsize(fmt)
         check(int, s)
+        # class
         s = vsize(fmt +                 # PyTypeObject
                   '3P'                  # PyAsyncMethods
                   '36P'                 # PyNumberMethods
@@ -1081,13 +1082,17 @@ class SizeofTest(unittest.TestCase):
                   '10P'                 # PySequenceMethods
                   '2P'                  # PyBufferProcs
                   '4P')
-        # Separate block for PyDictKeysObject with 8 keys and 5 entries
-        s += calcsize("2nP2n") + 8 + 5*calcsize("n2P")
-        # class
         class newstyleclass(object): pass
-        check(newstyleclass, s)
+        # Separate block for PyDictKeysObject with 8 keys and 5 entries
+        check(newstyleclass, s + calcsize("2nP2n0P") + 8 + 5*calcsize("n2P"))
+        # dict with shared keys
+        check(newstyleclass().__dict__, size('nQ2P') + 5*self.P)
+        o = newstyleclass()
+        o.a = o.b = o.c = o.d = o.e = o.f = o.g = o.h = 1
+        # Separate block for PyDictKeysObject with 16 keys and 10 entries
+        check(newstyleclass, s + calcsize("2nP2n0P") + 16 + 10*calcsize("n2P"))
         # dict with shared keys
-        check(newstyleclass().__dict__, size('nQ2P' + '2nP2n'))
+        check(newstyleclass().__dict__, size('nQ2P') + 10*self.P)
         # unicode
         # each tuple contains a string and its expected character size
         # don't put any static strings here, as they may contain