test: Assumeutxo: import snapshot in a node with a divergent chain

test/functional/feature_assumeutxo.py

@@ -17,16 +17,12 @@
       bad other serialization)
 - TODO: Valid snapshot file, but referencing a snapshot block that turns out to be
       invalid, or has an invalid parent
-- TODO: Valid snapshot file and snapshot block, but the block is not on the
-      most-work chain
 
 Interesting starting states could be loading a snapshot when the current chain tip is:
 
 - TODO: An ancestor of snapshot block
-- TODO: Not an ancestor of the snapshot block but has less work
 - TODO: The snapshot block
 - TODO: A descendant of the snapshot block
-- TODO: Not an ancestor or a descendant of the snapshot block and has more work
 
 """
 from shutil import rmtree
@@ -152,6 +148,38 @@ def test_invalid_mempool_state(self, dump_output_path):
 
         self.restart_node(2, extra_args=self.extra_args[2])
 
+    def test_snapshot_in_a_divergent_chain(self, dump_output_path):
+        # First rollback node2's chain to the pregenerated one, up to height 199
+        node = self.nodes[2]
+        current_height = node.getblockcount()
+        base_height = 199
+        for block_height in range(current_height, base_height, -1):
+            block_hash = node.getblockhash(block_height)
+            node.invalidateblock(block_hash)
+        assert_equal(node.getblockcount(), START_HEIGHT)
+
+        self.log.info(f"Check importing a snapshot where current chain-tip is not an ancestor of the snapshot block but has less work")
+        # Generate a totally different chain in node2 but with less work compared to the snapshot
+        self.generate(node, nblocks=99, sync_fun=self.no_op)
+        assert node.getblockcount() < SNAPSHOT_BASE_HEIGHT
+        # Try importing the snapshot and assert its success
+        loaded = node.loadtxoutset(dump_output_path)
+        assert_equal(loaded['coins_loaded'], SNAPSHOT_BASE_HEIGHT)
+        assert_equal(loaded['base_height'], SNAPSHOT_BASE_HEIGHT)
+
+        # Restart the node and delete the snapshot chainstate.
+        self.restart_node(2, extra_args=['-reindex-chainstate=1', *self.extra_args[2]])
+        assert_equal(node.getblockcount(), 298)
+
+        self.log.info(f"Check importing a snapshot where current chain-tip is not an ancestor or a descendant of the snapshot block and has more work")
+        # Generate two extra blocks and make sure node2's chain has more work than the snapshot's chain
+        # This covers the scenario where the snapshot block is not on the most-work chain
+        self.generate(node, nblocks=2, sync_fun=self.no_op)
+        assert node.getblockcount() > SNAPSHOT_BASE_HEIGHT
+        # Import the snapshot and assert its failure
+        with node.assert_debug_log(expected_msgs=["[snapshot] activation failed - work does not exceed active chainstate"]):
+            assert_raises_rpc_error(-32603, "Unable to load UTXO snapshot", node.loadtxoutset, dump_output_path)
+
     def run_test(self):
         """
         Bring up two (disconnected) nodes, mine some new blocks on the first,
@@ -365,10 +393,10 @@ def check_tx_counts(final: bool) -> None:
                 self.wait_until(lambda: n.getindexinfo() == completed_idx_state)
 
 
-        # Node 2: all indexes + reindex
-        # -----------------------------
+        # Node 2: all indexes + reindex + divergent chain
+        # -----------------------------------------------
 
-        self.log.info("-- Testing all indexes + reindex")
+        self.log.info("-- Testing all indexes + reindex + divergent chain")
         assert_equal(n2.getblockcount(), START_HEIGHT)
 
         self.log.info(f"Loading snapshot into third node from {dump_output['path']}")
@@ -434,6 +462,8 @@ def check_tx_counts(final: bool) -> None:
         self.connect_nodes(0, 2)
         self.wait_until(lambda: n2.getblockcount() == FINAL_HEIGHT)
 
+        self.test_snapshot_in_a_divergent_chain(dump_output['path'])
+
 @dataclass
 class Block:
     hash: str