Raise on timeout < 0 and re-add test case

Author: giampaolo

Lib/subprocess.py

@@ -2122,6 +2122,8 @@ def _wait(self, timeout):
                 return self.returncode
 
             if timeout is not None:
+                if timeout < 0:
+                    raise TimeoutExpired(self.args, timeout)
                 started = _time()
                 endtime = started + timeout
 

Lib/test/test_subprocess.py

@@ -163,6 +163,12 @@ def test_call_timeout(self):
                           timeout=0.1)
 
     def test_timeout_exception(self):
+        try:
+            subprocess.run([sys.executable, '-c', 'import time;time.sleep(9)'], timeout = -1)
+        except subprocess.TimeoutExpired as e:
+            self.assertIn("-1 seconds", str(e))
+        else:
+            self.fail("Expected TimeoutExpired exception not raised")
         try:
             subprocess.run([sys.executable, '-c', 'import time;time.sleep(9)'], timeout = 0)
         except subprocess.TimeoutExpired as e:

Misc/NEWS.d/next/Library/2026-01-19-16-45-16.gh-issue-83069.0TaeH9.rst

@@ -4,7 +4,7 @@ event-driven mechanism now waits for process termination, if available:
 - Linux ≥= 5.3 uses :func:`os.pidfd_open` + :func:`select.poll`
 - macOS and other BSD variants use :func:`select.kqueue` + ``KQ_FILTER_PROC`` +
   ``KQ_NOTE_EXIT``
-- Windows keep using ``WaitForSingleObject`` (unchanged)
+- Windows keeps using ``WaitForSingleObject`` (unchanged)
 
 If none of these mechanisms are available, the function falls back to the
 traditional busy loop (non-blocking call and short sleeps).