Adds a tiebrak test following PR 29284's description

test/functional/feature_chain_tiebreaks.py

@@ -0,0 +1,88 @@
+#!/usr/bin/env python3
+# Copyright (c) The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+"""Test that the correct active block is chosen in complex reorgs."""
+
+from test_framework.blocktools import create_block
+from test_framework.messages import CBlockHeader
+from test_framework.p2p import P2PDataStore
+from test_framework.test_framework import BitcoinTestFramework
+from test_framework.util import assert_equal
+
+class ChainTiebreaksTest(BitcoinTestFramework):
+    def set_test_params(self):
+        self.num_nodes = 2
+        self.setup_clean_chain = True
+
+    @staticmethod
+    def send_headers(node, blocks):
+        """Submit headers for blocks to node."""
+        for block in blocks:
+            # Use RPC rather than P2P, to prevent the message from being interpreted as a block
+            # announcement.
+            node.submitheader(hexdata=CBlockHeader(block).serialize().hex())
+
+    def run_test(self):
+        node = self.nodes[0]
+        # Add P2P connection to bitcoind
+        peer = node.add_p2p_connection(P2PDataStore())
+
+        self.log.info('Precomputing blocks')
+        #
+        #       B  - C
+        #      /  
+        #    A
+        #      \  
+        #       B' - C'
+        #
+        blocks = []
+
+        # Construct A, building off genesis.
+        start_height = node.getblockcount()
+        blocks.append(create_block(
+            hashprev=int(node.getbestblockhash(), 16),
+            tmpl={"height": start_height + 1}
+        ))
+        blocks[-1].solve()
+
+        # Construct all blocks.
+        for i in range(0, 4):
+            if i%2==0:
+                prev_idx = 0
+            else:
+                prev_idx = len(blocks) - 1
+
+            blocks.append(create_block(
+            hashprev=int(blocks[prev_idx].hash, 16),
+            tmpl={
+                "height": start_height + 1 + (i % 2) + 1,
+                # Make sure each block has a different hash.
+                "curtime": blocks[-1].nTime + 1,
+            }
+            ))
+            blocks[-1].solve()
+
+        self.log.info('Make sure A is accepted normally')
+        peer.send_blocks_and_test([blocks[0]], node, success=True)
+        # A must be active chain now.
+        assert_equal(node.getbestblockhash(), blocks[0].hash)
+
+        self.log.info('Send B header and C')
+        self.send_headers(node, [blocks[1]])
+        peer.send_blocks_and_test([blocks[2]], node, success=False)
+
+        # A must still be the active chain, given we only have the header of B (therefore C cannot be connected)
+        assert_equal(node.getbestblockhash(), blocks[0].hash)
+
+        self.log.info("Send B' and C'")
+        peer.send_blocks_and_test(blocks[3:], node, success=True)
+        # C' should be the active chain
+        assert_equal(node.getbestblockhash(), blocks[4].hash)
+
+        self.log.info("Send B and check that the active chain is still C'")
+        peer.send_blocks_and_test([blocks[1]], node, success=False)
+        assert_equal(node.getbestblockhash(), blocks[4].hash)
+
+if __name__ == '__main__':
+    ChainTiebreaksTest().main()

test/functional/test_runner.py

@@ -358,6 +358,7 @@
     'feature_includeconf.py',
     'feature_addrman.py',
     'feature_asmap.py',
+    'feature_chain_tiebreaks.py',
     'feature_fastprune.py',
     'mempool_unbroadcast.py',
     'mempool_compatibility.py',