fix test_python_legacy_windows_stdio

Author: methane

Lib/test/test_cmd_line.py

@@ -972,10 +972,32 @@ def test_python_legacy_windows_fs_encoding(self):
 
     @unittest.skipUnless(support.MS_WINDOWS, 'Test only applicable on Windows')
     def test_python_legacy_windows_stdio(self):
-        code = "import sys; print(sys.stdin.encoding, sys.stdout.encoding)"
-        expected = 'cp'
-        rc, out, err = assert_python_ok('-c', code, PYTHONLEGACYWINDOWSSTDIO='1')
-        self.assertIn(expected.encode(), out)
+        fn = os_helper.TESTFN
+        # We cannot use PIPE to test ConsoleIO
+        code = dedent(f"""
+        import sys
+        with open({fn!r}, 'w', encoding='utf-8') as f:
+            print(type(sys.stdout.buffer.raw).__name__, file=f)
+        """)
+
+        # Test that _WindowsConsoleIO is used when PYTHONLEGACYWINDOWSSTDIO is not set.
+        subprocess.run([sys.executable, "-c", code], check=True,
+                       creationflags=subprocess.CREATE_NEW_CONSOLE)
+        with open(fn, "r", encoding="utf-8") as f:
+            out = f.read()
+        os.remove(fn)
+        self.assertEqual(out.strip(), "_WindowsConsoleIO")
+
+        # Test that _FileIO is used when PYTHONLEGACYWINDOWSSTDIO is set.
+        env = os.environ.copy()
+        env["PYTHONLEGACYWINDOWSSTDIO"] = "1"
+        subprocess.run([sys.executable, "-c", code], check=True,
+                       creationflags=subprocess.CREATE_NEW_CONSOLE,
+                       env=env)
+        with open(fn, "r", encoding="utf-8") as f:
+            out = f.read()
+        os.remove(fn)
+        self.assertEqual(out.strip(), "FileIO")
 
     @unittest.skipIf("-fsanitize" in sysconfig.get_config_vars().get('PY_CFLAGS', ()),
                      "PYTHONMALLOCSTATS doesn't work with ASAN")