Make test more reliable.

Author: serhiy-storchaka

Lib/importlib/_bootstrap_external.py

@@ -762,7 +762,7 @@ def _validate_timestamp_pyc(self, data, source_mtime, source_size, name,
             pass
         else:
             if bytecode_mtime < source_mtime:
-                message = f'bytecode may be stale for {name!r}'
+                message = f'bytecode is stale for {name!r}'
                 _bootstrap._verbose_message('{}', message)
                 raise ImportError(message, **exc_details)
 

Lib/test/test_import/__init__.py

@@ -1523,25 +1523,28 @@ def test_recompute_pyc_same_second_same_size(self):
         # to seconds) and size, the difference between the source and
         # the bytecode timestamps is enough to trigger recomputation of
         # the pyc file.
-        prev_mtime = 0
+        pyc_file = importlib.util.cache_from_source(self.source)
         for i in range(10, 100):
-            with self.subTest(i):
-                while True:
-                    with open(self.source, 'w', encoding='utf-8') as fp:
-                        print(f"x = {i}", file=fp)
-                    mtime = os.stat(self.source).st_mtime
-                    if mtime > prev_mtime:
-                        break
-                    time.sleep(1e-3)
-                self.assertGreater(mtime, prev_mtime)
-                prev_mtime = mtime
-
-                m = __import__(TESTFN)
-                self.assertEqual(m.x, i)
-                unload(TESTFN)
-                m = __import__(TESTFN)
-                self.assertEqual(m.x, i)
-                unload(TESTFN)
+            try:
+                bytecode_mtime = os.stat(pyc_file).st_mtime
+            except FileNotFoundError:
+                # The pyc file has not yet be created.
+                bytecode_mtime = 0
+            delay = 1e-3
+            for j in range(10):
+                time.sleep(delay)
+                with open(self.source, 'w', encoding='utf-8') as fp:
+                    print(f"x = {i}", file=fp)
+                if os.stat(self.source).st_mtime > bytecode_mtime:
+                    break
+                delay *= 2
+
+            m = __import__(TESTFN)
+            self.assertEqual(m.x, i)
+            unload(TESTFN)
+            m = __import__(TESTFN)
+            self.assertEqual(m.x, i)
+            unload(TESTFN)
 
 
 class TestSymbolicallyLinkedPackage(unittest.TestCase):