[3.13] gh-120683: Fix an error in logging.LogRecord timestamp (GH-120709) (GH-120933)

The integer part of the timestamp can be rounded up, while the millisecond
calculation truncates, causing the log timestamp to be wrong by up to 999 ms
(affected roughly 1 in 8 million timestamps).
(cherry picked from commit 1500a23f33f5a6d052ff1ef6383d9839928b8ff1)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

1 files changed, 7 insertions, 2 deletions

diff --git a/Lib/test/test_logging.py b/Lib/test/test_logging.py
index 504862a..c78e76d 100644
--- a/Lib/test/test_logging.py
+++ b/Lib/test/test_logging.py
@@ -4648,13 +4648,18 @@ class FormatterTest(unittest.TestCase, AssertErrorMessage):
             (1_677_902_297_100_000_000, 100.0),  # exactly 100ms
             (1_677_903_920_999_998_503, 999.0),  # check truncating doesn't round
             (1_677_903_920_000_998_503, 0.0),  # check truncating doesn't round
+            (1_677_903_920_999_999_900, 0.0), # check rounding up
         )
         for ns, want in tests:
             with patch('time.time_ns') as patched_ns:
                 patched_ns.return_value = ns
                 record = logging.makeLogRecord({'msg': 'test'})
-            self.assertEqual(record.msecs, want)
-            self.assertEqual(record.created, ns / 1e9)
+            with self.subTest(ns):
+                self.assertEqual(record.msecs, want)
+                self.assertEqual(record.created, ns / 1e9)
+                self.assertAlmostEqual(record.created - int(record.created),
+                                       record.msecs / 1e3,
+                                       delta=1e-3)
 
     def test_relativeCreated_has_higher_precision(self):
         # See issue gh-102402.