test: Add bitcoin-chainstate test for assumeutxo functionality

diff --git a/src/kernel/chainparams.cpp b/src/kernel/chainparams.cpp
index 50891a8d..300df95f 100644
--- a/src/kernel/chainparams.cpp
+++ b/src/kernel/chainparams.cpp
@@ -638,7 +638,7 @@ public:
                 .blockhash = consteval_ctor(uint256{"385901ccbd69dff6bbd00065d01fb8a9e464dede7cfe0372443884f9b1dcf6b9"}),
             },
             {
-                // For use by test/functional/feature_assumeutxo.py
+                // For use by test/functional/feature_assumeutxo.py and test/functional/tool_bitcoin_chainstate.py
                 .height = 299,
                 .hash_serialized = AssumeutxoHash{uint256{"d2b051ff5e8eef46520350776f4100dd710a63447a8e01d917e92e79751a63e2"}},
                 .m_chain_tx_count = 334,
diff --git a/test/functional/tool_bitcoin_chainstate.py b/test/functional/tool_bitcoin_chainstate.py
index 7795b20d..8f33da35 100755
--- a/test/functional/tool_bitcoin_chainstate.py
+++ b/test/functional/tool_bitcoin_chainstate.py
@@ -2,25 +2,58 @@
 # Copyright (c) 2022-present 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 bitcoin-chainstate tool functionality
+
+Test basic block processing via bitcoin-chainstate tool, including detecting
+duplicates and malformed input.
+
+Test that bitcoin-chainstate can load a datadir initialized with an assumeutxo
+snapshot and extend the snapshot chain with new blocks.
+"""
 
 import subprocess
 
 from test_framework.test_framework import BitcoinTestFramework
+from test_framework.util import assert_equal
+from test_framework.wallet import MiniWallet
+
+START_HEIGHT = 199
+# Hardcoded in regtest chainparams
+SNAPSHOT_BASE_BLOCK_HEIGHT = 299
+SNAPSHOT_BASE_BLOCK_HASH = "7cc695046fec709f8c9394b6f928f81e81fd3ac20977bb68760fa1faa7916ea2"
+
 
 class BitcoinChainstateTest(BitcoinTestFramework):
     def skip_test_if_missing_module(self):
         self.skip_if_no_bitcoin_chainstate()
 
     def set_test_params(self):
-        self.setup_clean_chain = True
-        self.chain = ""
-        self.num_nodes = 1
-        # Set prune to avoid disk space warning.
-        self.extra_args = [["-prune=550"]]
+        """Use the pregenerated, deterministic chain up to height 199."""
+        self.num_nodes = 2
 
-    def add_block(self, datadir, input, expected_stderr):
+    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(2)
+        self.start_nodes()
+
+    def generate_snapshot_chain(self):
+        self.log.info(f"Generate deterministic chain up to block {SNAPSHOT_BASE_BLOCK_HEIGHT} for node0 while node1 disconnected")
+        n0 = self.nodes[0]
+        assert_equal(n0.getblockcount(), START_HEIGHT)
+        n0.setmocktime(n0.getblockheader(n0.getbestblockhash())['time'])
+        mini_wallet = MiniWallet(n0)
+        for i in range(SNAPSHOT_BASE_BLOCK_HEIGHT - n0.getblockchaininfo()["blocks"]):
+            if i % 3 == 0:
+                mini_wallet.send_self_transfer(from_node=n0)
+            self.generate(n0, nblocks=1, sync_fun=self.no_op)
+        assert_equal(n0.getblockcount(), SNAPSHOT_BASE_BLOCK_HEIGHT)
+        assert_equal(n0.getbestblockhash(), SNAPSHOT_BASE_BLOCK_HASH)
+        return n0.dumptxoutset('utxos.dat', "latest")
+
+    def add_block(self, datadir, input, expected_stderr=None, expected_stdout=None):
         proc = subprocess.Popen(
-            self.get_binaries().chainstate_argv() + [datadir],
+            self.get_binaries().chainstate_argv() + ["-regtest", datadir],
             stdin=subprocess.PIPE,
             stdout=subprocess.PIPE,
             stderr=subprocess.PIPE,
@@ -30,20 +63,44 @@ class BitcoinChainstateTest(BitcoinTestFramework):
         self.log.debug("STDOUT: {0}".format(stdout.strip("\n")))
         self.log.info("STDERR: {0}".format(stderr.strip("\n")))
 
-        if expected_stderr not in stderr:
-            raise AssertionError(f"Expected stderr output {expected_stderr} does not partially match stderr:\n{stderr}")
+        if expected_stderr is not None and expected_stderr not in stderr:
+            raise AssertionError(f"Expected stderr output '{expected_stderr}' does not partially match stderr:\n{stderr}")
+        if expected_stdout is not None and expected_stdout not in stdout:
+            raise AssertionError(f"Expected stdout output '{expected_stdout}' does not partially match stdout:\n{stdout}")
+
+    def basic_test(self):
+        n0 = self.nodes[0]
+        n1 = self.nodes[1]
+        datadir = n1.chain_path
+        n1.stop_node()
+        block = n0.getblock(n0.getblockhash(START_HEIGHT+1), 0)
+        self.log.info(f"Test bitcoin-chainstate {self.get_binaries().chainstate_argv()} with datadir: {datadir}")
+        self.add_block(datadir, block, expected_stderr="Block has not yet been rejected")
+        self.add_block(datadir, block, expected_stderr="duplicate")
+        self.add_block(datadir, "00", expected_stderr="Block decode failed")
+        self.add_block(datadir, "", expected_stderr="Empty line found")
+
+    def assumeutxo_test(self, dump_output_path):
+        n0 = self.nodes[0]
+        n1 = self.nodes[1]
+        self.start_node(1)
+        self.log.info("Submit headers for new blocks to node1, then load the snapshot so it activates")
+        for height in range(START_HEIGHT+2, SNAPSHOT_BASE_BLOCK_HEIGHT+1):
+            block = n0.getblock(n0.getblockhash(height), 0)
+            n1.submitheader(block)
+        assert_equal(n1.getblockcount(), START_HEIGHT+1)
+        loaded = n1.loadtxoutset(dump_output_path)
+        assert_equal(loaded['base_height'], SNAPSHOT_BASE_BLOCK_HEIGHT)
+        datadir = n1.chain_path
+        n1.stop_node()
+        self.log.info(f"Test bitcoin-chainstate {self.get_binaries().chainstate_argv()} with an assumeutxo datadir: {datadir}")
+        new_tip_hash = self.generate(n0, nblocks=1, sync_fun=self.no_op)[0]
+        self.add_block(datadir, n0.getblock(new_tip_hash, 0), expected_stdout="Block tip changed")
 
     def run_test(self):
-        node = self.nodes[0]
-        datadir = node.cli.datadir
-        node.stop_node()
-
-        self.log.info(f"Testing bitcoin-chainstate {self.get_binaries().chainstate_argv()} with datadir: {datadir}")
-        block_one = "010000006fe28c0ab6f1b372c1a6a246ae63f74f931e8365e15a089c68d6190000000000982051fd1e4ba744bbbe680e1fee14677ba1a3c3540bf7b1cdb606e857233e0e61bc6649ffff001d01e362990101000000010000000000000000000000000000000000000000000000000000000000000000ffffffff0704ffff001d0104ffffffff0100f2052a0100000043410496b538e853519c726a2c91e61ec11600ae1390813a627c66fb8be7947be63c52da7589379515d4e0a604f8141781e62294721166bf621e73a82cbf2342c858eeac00000000"
-        self.add_block(datadir, block_one, "Block has not yet been rejected")
-        self.add_block(datadir, block_one, "duplicate")
-        self.add_block(datadir, "00", "Block decode failed")
-        self.add_block(datadir, "", "Empty line found")
+        dump_output = self.generate_snapshot_chain()
+        self.basic_test()
+        self.assumeutxo_test(dump_output['path'])
 
 if __name__ == "__main__":
     BitcoinChainstateTest(__file__).main()