test: loading assumeutxo snapshot with current chaintip

at snapshot base height

test/functional/feature_assumeutxo.py

@@ -27,7 +27,6 @@
 
 - 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
 
@@ -55,18 +54,19 @@ class AssumeutxoTest(BitcoinTestFramework):
 
     def set_test_params(self):
         """Use the pregenerated, deterministic chain up to height 199."""
-        self.num_nodes = 3
+        self.num_nodes = 4
         self.rpc_timeout = 120
         self.extra_args = [
             [],
             ["-fastprune", "-prune=1", "-blockfilterindex=1", "-coinstatsindex=1"],
             ["-persistmempool=0","-txindex=1", "-blockfilterindex=1", "-coinstatsindex=1"],
+            [],
         ]
 
     def setup_network(self):
         """Start with the nodes disconnected so that one can generate a snapshot
         including blocks the other hasn't yet seen."""
-        self.add_nodes(3)
+        self.add_nodes(4)
         self.start_nodes(extra_args=self.extra_args)
 
     def test_invalid_snapshot_scenarios(self, valid_snapshot_path):
@@ -148,6 +148,21 @@ def test_invalid_mempool_state(self, dump_output_path):
 
         self.restart_node(2, extra_args=self.extra_args[2])
 
+    def test_loading_snapshot_at_snapshot_base_height(self, dump_output_path):
+        self.log.info("Test loading snapshot with current chain tip at SNAPSHOT_BASE_HEIGHT (h=299)")
+
+        n0 = self.nodes[0]
+        n3 = self.nodes[3]
+
+        self.connect_nodes(0,3)
+        self.wait_until(lambda: n3.getchainstates()['chainstates'][-1]['blocks'] == SNAPSHOT_BASE_HEIGHT)
+        self.sync_blocks(nodes=(n0, n3))
+        assert_equal(n3.getblockcount(), SNAPSHOT_BASE_HEIGHT)
+
+        # Attempt to load the snapshot at SNAPSHOT_BASE_HEIGHT (h=299)
+        with n3.assert_debug_log(expected_msgs=["[snapshot] activation failed - work does not exceed active chainstate"]):
+            assert_raises_rpc_error(-32603, "Unable to load UTXO snapshot", n3.loadtxoutset, dump_output_path)
+
     def run_test(self):
         """
         Bring up two (disconnected) nodes, mine some new blocks on the first,
@@ -159,6 +174,7 @@ def run_test(self):
         n0 = self.nodes[0]
         n1 = self.nodes[1]
         n2 = self.nodes[2]
+        n3 = self.nodes[3]
 
         self.mini_wallet = MiniWallet(n0)
 
@@ -182,6 +198,7 @@ def run_test(self):
             # make n1 aware of the new header, but don't give it the block.
             n1.submitheader(newblock)
             n2.submitheader(newblock)
+            n3.submitheader(newblock)
 
         # Ensure everyone is seeing the same headers.
         for n in self.nodes:
@@ -201,6 +218,9 @@ def run_test(self):
         assert_equal(dump_output["nchaintx"], 334)
         assert_equal(n0.getblockchaininfo()["blocks"], SNAPSHOT_BASE_HEIGHT)
 
+        self.test_loading_snapshot_at_snapshot_base_height(dump_output['path'])
+
+
         # Mine more blocks on top of the snapshot that n1 hasn't yet seen. This
         # will allow us to test n1's sync-to-tip on top of a snapshot.
         self.generate(n0, nblocks=100, sync_fun=self.no_op)