Fix test_cmd_line fail with PYTHONUNBUFFERED=1

Author: WolframAlph

Lib/test/test_cmd_line.py

@@ -1175,7 +1175,15 @@ def test_decoding_error_at_the_end_of_the_line(self):
         self.check_string(br"'\u1f'")
 
 
+PYTHONUNBUFFERED_ENV_VAR = os.environ["PYTHONUNBUFFERED"]
+
+def setUpModule():
+    # we expect buffered stdio
+    os.environ["PYTHONUNBUFFERED"] = "0"
+
 def tearDownModule():
+    # restore original value
+    os.environ["PYTHONUNBUFFERED"] = PYTHONUNBUFFERED_ENV_VAR
     support.reap_children()