gh-158895: Teach librertest to output github job summaries

Goal is to make it faster to triage individual test failures while
keeping the full existing regrtest fidelity. Fairly minimal integration
to hopefully save some human eyeball time.

Setup so only the test summary process should output the summary,
subprocesses have the env var which will cause output unset.

Author: cmaloney

Lib/test/libregrtest/main.py

@@ -1,3 +1,5 @@
+import contextlib
+import io
 import os
 import random
 import re
@@ -6,7 +8,7 @@
 import sysconfig
 import time
 import trace
-from _colorize import get_colors  # type: ignore[import-not-found]
+from _colorize import decolor, get_colors  # type: ignore[import-not-found]
 from typing import NoReturn
 
 from test.support import os_helper, MS_WINDOWS, flush_std_streams
@@ -480,6 +482,25 @@ def finalize_tests(self, coverage: trace.CoverageResults | None) -> None:
         if self.junit_filename:
             self.results.write_junit(self.junit_filename)
 
+        self.write_github_summary()
+
+    def write_github_summary(self) -> None:
+        filename = os.environ.get("GITHUB_STEP_SUMMARY")
+        if not filename:
+            return
+        with contextlib.redirect_stdout(io.StringIO()) as summary:
+            self.display_summary()
+        lines = ["## Test results",
+                 f"```\n{decolor(summary.getvalue()).strip()}\n```"]
+        # Tests which failed in the last run (the re-run, if any)
+        for result in self.results.rerun_results:
+            lines.append(f"### {decolor(str(result))}")
+            for name, traceback in (result.errors or []) + (result.failures or []):
+                lines.append(f"<details><summary>{name}</summary>\n\n"
+                             f"```\n{traceback}\n```\n</details>")
+        with open(filename, "a", encoding="utf-8") as fp:
+            fp.write("\n\n".join(lines) + "\n")
+
     def display_summary(self) -> None:
         if self.first_runtests is None:
             raise ValueError(

Lib/test/libregrtest/worker.py

@@ -28,6 +28,8 @@ def create_worker_process(runtests: WorkerRunTests, output_fd: int,
     cmd.extend(['-m', 'test.libregrtest.worker', worker_json])
 
     env = dict(os.environ)
+    # Only the main process writes the GitHub Actions job summary
+    env.pop('GITHUB_STEP_SUMMARY', None)
     if tmp_dir is not None:
         env['TMPDIR'] = tmp_dir
         env['TEMP'] = tmp_dir

Misc/NEWS.d/next/Tests/2026-10-05-22-36-06.gh-issue-158895.3Dmc4J.rst

@@ -0,0 +1,2 @@
+Individual test failures and an overall summary is now written by
+:mod:`test.regrtest` to the Github Action Summary.