From 0c5ad5499798aed4cd305d324051986ed4c48c8c Mon Sep 17 00:00:00 2001
From: Curtis Bucher <cpbucher5@gmail.com>
Date: Mon, 30 Mar 2020 09:50:57 -0700
Subject: [PATCH] Fix bug in test_collections.py (#19221)

Test in TestChainMap() line 257 did not properly check union behavior.
---
 Lib/test/test_collections.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Lib/test/test_collections.py b/Lib/test/test_collections.py
index 47c500bcdd0..0207823f5aa 100644
--- a/Lib/test/test_collections.py
+++ b/Lib/test/test_collections.py
@@ -253,8 +253,9 @@ class TestChainMap(unittest.TestCase):
         # testing behavior between chainmap and iterable key-value pairs
         with self.assertRaises(TypeError):
             cm3 | pairs
+        tmp = cm3.copy()
         cm3 |= pairs
-        self.assertEqual(cm3.maps, [cm3.maps[0] | dict(pairs), *cm3.maps[1:]])
+        self.assertEqual(cm3.maps, [tmp.maps[0] | dict(pairs), *tmp.maps[1:]])
 
         # testing proper return types for ChainMap and it's subclasses
         class Subclass(ChainMap):