gh-84649: Fix unstable test_rollover_at_midnight (GH-151813)

The test forced a rollover by back-dating the file modification time, but
the rollover time is now based also on the creation time, which cannot be
changed.  Instead, set the rollover time one second after the file
creation time and wait until the clock reaches it.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: serhiy-storchaka

Lib/test/test_logging.py

@@ -6705,20 +6705,18 @@ def add_record(message: str) -> None:
 
     def test_rollover_at_midnight(self, weekly=False):
         os_helper.unlink(self.fn)
+        # Emit the first records a little after the beginning of a whole
+        # second, so that their file times fall inside that second and not the
+        # previous one, which would cause an unwanted rollover.
         now = datetime.datetime.now()
-        atTime = now.time()
-        if not 0.1 < atTime.microsecond/1e6 < 0.9:
-            # The test requires all records to be emitted within
-            # the range of the same whole second.
-            time.sleep((0.1 - atTime.microsecond/1e6) % 1.0)
+        if not 0.1 < now.microsecond/1e6 < 0.9:
+            time.sleep((0.1 - now.microsecond/1e6) % 1.0)
             now = datetime.datetime.now()
-            atTime = now.time()
-        atTime = atTime.replace(microsecond=0)
         fmt = logging.Formatter('%(asctime)s %(message)s')
         when = f'W{now.weekday()}' if weekly else 'MIDNIGHT'
         for i in range(3):
             fh = logging.handlers.TimedRotatingFileHandler(
-                self.fn, encoding="utf-8", when=when, atTime=atTime)
+                self.fn, encoding="utf-8", when=when, atTime=now.time())
             fh.setFormatter(fmt)
             r2 = logging.makeLogRecord({'msg': f'testing1 {i}'})
             fh.emit(r2)
@@ -6728,15 +6726,22 @@ def test_rollover_at_midnight(self, weekly=False):
             for i, line in enumerate(f):
                 self.assertIn(f'testing1 {i}', line)
 
-        os.utime(self.fn, (now.timestamp() - 1,)*2)
+        # The creation time, used to compute the rollover time, cannot be
+        # changed, so the rollover cannot be forced by back-dating the file.
+        # Wait until the clock reaches a rollover time set one second ahead.
+        rollover = int(time.time()) + 1
+        atTime = datetime.datetime.fromtimestamp(rollover).time()
+        while time.time() < rollover:
+            time.sleep(rollover - time.time())
         for i in range(2):
             fh = logging.handlers.TimedRotatingFileHandler(
                 self.fn, encoding="utf-8", when=when, atTime=atTime)
             fh.setFormatter(fmt)
             r2 = logging.makeLogRecord({'msg': f'testing2 {i}'})
             fh.emit(r2)
             fh.close()
-        rolloverDate = now - datetime.timedelta(days=7 if weekly else 1)
+        rolloverDate = (datetime.datetime.fromtimestamp(rollover)
+                        - datetime.timedelta(days=7 if weekly else 1))
         otherfn = f'{self.fn}.{rolloverDate:%Y-%m-%d}'
         self.assertLogFile(otherfn)
         with open(self.fn, encoding="utf-8") as f: