bpo-40116: dict: Add regression test for iteration order. (GH-31550)

1 files changed, 17 insertions, 0 deletions

diff --git a/Lib/test/test_dict.py b/Lib/test/test_dict.py
index 66f5d56..e60ae43 100644
--- a/Lib/test/test_dict.py
+++ b/Lib/test/test_dict.py
@@ -1077,6 +1077,23 @@ class DictTest(unittest.TestCase):
         self.assertEqual(list(a), ['x', 'y'])
         self.assertEqual(list(b), ['x', 'y', 'z'])
 
+    @support.cpython_only
+    def test_splittable_update(self):
+        """dict.update(other) must preserve order in other."""
+        class C:
+            def __init__(self, order):
+                if order:
+                    self.a, self.b, self.c = 1, 2, 3
+                else:
+                    self.c, self.b, self.a = 1, 2, 3
+        o = C(True)
+        o = C(False)  # o.__dict__ has reversed order.
+        self.assertEqual(list(o.__dict__), ["c", "b", "a"])
+
+        d = {}
+        d.update(o.__dict__)
+        self.assertEqual(list(d), ["c", "b", "a"])
+
     def test_iterator_pickling(self):
         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
             data = {1:"a", 2:"b", 3:"c"}