[3.6] bpo-30441: Fix bug when modifying os.environ while iterating over it (GH-2409). (#2556)

(cherry picked from commit 8a8d28501fc8ce25926d168f1c657656c809fd4c)

1 files changed, 24 insertions, 0 deletions

diff --git a/Lib/test/test_os.py b/Lib/test/test_os.py
index fdeb9a9..f74c199 100644
--- a/Lib/test/test_os.py
+++ b/Lib/test/test_os.py
@@ -836,6 +836,30 @@ class EnvironTests(mapping_tests.BasicTestMappingProtocol):
         self.assertIs(cm.exception.args[0], missing)
         self.assertTrue(cm.exception.__suppress_context__)
 
+    def _test_environ_iteration(self, collection):
+        iterator = iter(collection)
+        new_key = "__new_key__"
+
+        next(iterator)  # start iteration over os.environ.items
+
+        # add a new key in os.environ mapping
+        os.environ[new_key] = "test_environ_iteration"
+
+        try:
+            next(iterator)  # force iteration over modified mapping
+            self.assertEqual(os.environ[new_key], "test_environ_iteration")
+        finally:
+            del os.environ[new_key]
+
+    def test_iter_error_when_changing_os_environ(self):
+        self._test_environ_iteration(os.environ)
+
+    def test_iter_error_when_changing_os_environ_items(self):
+        self._test_environ_iteration(os.environ.items())
+
+    def test_iter_error_when_changing_os_environ_values(self):
+        self._test_environ_iteration(os.environ.values())
+
 
 class WalkTests(unittest.TestCase):
     """Tests for os.walk()."""