Issue #19800: make the pickle framing tests more precise.

Lib/test/pickletester.py

@@ -1416,6 +1416,26 @@ class AbstractPickleTests(unittest.TestCase):
 
     FRAME_SIZE_TARGET = 64 * 1024
 
+    def check_frame_opcodes(self, pickled):
+        """
+        Check the arguments of FRAME opcodes in a protocol 4+ pickle.
+        """
+        frame_opcode_size = 9
+        last_arg = last_pos = None
+        for op, arg, pos in pickletools.genops(pickled):
+            if op.name != 'FRAME':
+                continue
+            if last_pos is not None:
+                # The previous frame's size should be equal to the number
+                # of bytes up to the current frame.
+                frame_size = pos - last_pos - frame_opcode_size
+                self.assertEqual(frame_size, last_arg)
+            last_arg, last_pos = arg, pos
+        # The last frame's size should be equal to the number of bytes up
+        # to the pickle's end.
+        frame_size = len(pickled) - last_pos - frame_opcode_size
+        self.assertEqual(frame_size, last_arg)
+
     def test_framing_many_objects(self):
         obj = list(range(10**5))
         for proto in range(4, pickle.HIGHEST_PROTOCOL + 1):
@@ -1429,6 +1449,7 @@ class AbstractPickleTests(unittest.TestCase):
                                    self.FRAME_SIZE_TARGET / 2)
                 self.assertLessEqual(bytes_per_frame,
                                      self.FRAME_SIZE_TARGET * 1)
+                self.check_frame_opcodes(pickled)
 
     def test_framing_large_objects(self):
         N = 1024 * 1024
@@ -1440,6 +1461,7 @@ class AbstractPickleTests(unittest.TestCase):
                 self.assertEqual(obj, unpickled)
                 n_frames = count_opcode(pickle.FRAME, pickled)
                 self.assertGreaterEqual(n_frames, len(obj))
+                self.check_frame_opcodes(pickled)
 
     def test_optional_frames(self):
         if pickle.HIGHEST_PROTOCOL < 4: