bpo-31479: Always reset the signal alarm in tests (GH-3588) (GH-7312)

* bpo-31479: Always reset the signal alarm in tests

Use "try: ... finally: signal.signal(0)" pattern to make sure that
tests don't "leak" a pending fatal signal alarm.

* Move two more alarm() calls into the try block

Fix also typo: replace signal.signal(0) with signal.alarm(0)

* Move another signal.alarm() into the try block

(cherry picked from commit 9abee722d448c1c00c7d4e11ce242ec7b13e5c49)

1 files changed, 3 insertions, 6 deletions

diff --git a/Lib/test/test_pty.py b/Lib/test/test_pty.py
index 45ebea5..cd934bf 100644
--- a/Lib/test/test_pty.py
+++ b/Lib/test/test_pty.py
@@ -69,14 +69,11 @@ class PtyTest(unittest.TestCase):
     def setUp(self):
         # isatty() and close() can hang on some platforms.  Set an alarm
         # before running the test to make sure we don't hang forever.
-        self.old_alarm = signal.signal(signal.SIGALRM, self.handle_sig)
+        old_alarm = signal.signal(signal.SIGALRM, self.handle_sig)
+        self.addCleanup(signal.signal, signal.SIGALRM, old_alarm)
+        self.addCleanup(signal.alarm, 0)
         signal.alarm(10)
 
-    def tearDown(self):
-        # remove alarm, restore old alarm handler
-        signal.alarm(0)
-        signal.signal(signal.SIGALRM, self.old_alarm)
-
     def handle_sig(self, sig, frame):
         self.fail("isatty hung")