From eb1fe9003367fcf1134918efe20084df340435d2 Mon Sep 17 00:00:00 2001
From: Steve Dower <steve.dower@python.org>
Date: Wed, 7 Sep 2022 23:44:29 +0100
Subject: [PATCH] gh-95027: Ensure test runner uses utf-8:surrogateescape for
 communicating with subprocesses

---
 Lib/test/libregrtest/main.py                                  | 4 ++++
 Lib/test/libregrtest/runtest_mp.py                            | 4 +++-
 .../next/Tests/2022-09-07-23-44-06.gh-issue-95027.H5xs9o.rst  | 2 ++
 3 files changed, 9 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Tests/2022-09-07-23-44-06.gh-issue-95027.H5xs9o.rst

diff --git a/Lib/test/libregrtest/main.py b/Lib/test/libregrtest/main.py
index 655e4d2e56f8f04..e94e5eb86b2d20c 100644
--- a/Lib/test/libregrtest/main.py
+++ b/Lib/test/libregrtest/main.py
@@ -681,6 +681,10 @@ def main(self, tests=None, **kwargs):
 
         self.fix_umask()
 
+        # We may have been launched with a certain IO encoding, but we do not
+        # want children to inherit it, so clear it out now.
+        os.unsetenv('PYTHONIOENCODING')
+
         if self.ns.cleanup:
             self.cleanup()
             sys.exit(0)
diff --git a/Lib/test/libregrtest/runtest_mp.py b/Lib/test/libregrtest/runtest_mp.py
index a4d3e5c3146a8cf..5bab4e580b74c75 100644
--- a/Lib/test/libregrtest/runtest_mp.py
+++ b/Lib/test/libregrtest/runtest_mp.py
@@ -66,7 +66,9 @@ def run_test_in_subprocess(testname: str, ns: Namespace, tmp_dir: str, stdout_fh
            '-m', 'test.regrtest',
            '--worker-args', worker_args]
 
+
     env = dict(os.environ)
+    env['PYTHONIOENCODING'] = 'utf-8:surrogateescape'
     if tmp_dir is not None:
         env['TMPDIR'] = tmp_dir
         env['TEMP'] = tmp_dir
@@ -270,7 +272,7 @@ def _runtest(self, test_name: str) -> MultiprocessResult:
         # gh-94026: Write stdout+stderr to a tempfile as workaround for
         # non-blocking pipes on Emscripten with NodeJS.
         with tempfile.TemporaryFile(
-            'w+', encoding=sys.stdout.encoding
+            'w+', encoding=sys.stdout.encoding, errors="surrogateescape",
         ) as stdout_fh:
             # gh-93353: Check for leaked temporary files in the parent process,
             # since the deletion of temporary files can happen late during
diff --git a/Misc/NEWS.d/next/Tests/2022-09-07-23-44-06.gh-issue-95027.H5xs9o.rst b/Misc/NEWS.d/next/Tests/2022-09-07-23-44-06.gh-issue-95027.H5xs9o.rst
new file mode 100644
index 000000000000000..0453978818153d1
--- /dev/null
+++ b/Misc/NEWS.d/next/Tests/2022-09-07-23-44-06.gh-issue-95027.H5xs9o.rst
@@ -0,0 +1,2 @@
+Ensures test runner uses UTF-8 and surrogateescape encoding when
+communicating between multiple processes.