test: Add functional test for mnauth service guard

Co-authored-by: OpenAI Codex <codex@openai.com>

Author: UdjinM6

test/functional/p2p_mnauth.py

@@ -0,0 +1,56 @@
+#!/usr/bin/env python3
+# Copyright (c) 2026 The Dash Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+"""
+Test MNAUTH emission on the registered masternode service only.
+"""
+
+from test_framework.test_framework import (
+    DashTestFramework,
+    MasternodeInfo,
+)
+from test_framework.util import (
+    assert_equal,
+    p2p_port,
+)
+
+
+class P2PMNAUTHTest(DashTestFramework):
+    def add_options(self, parser):
+        self.add_wallet_options(parser)
+
+    def set_test_params(self):
+        self.alt_port = p2p_port(10)
+        self.mn_port = p2p_port(2)
+        self.set_dash_test_params(3, 1, extra_args=[
+            [],
+            [],
+            [f"-bind=127.0.0.1:{self.alt_port}", f"-externalip=127.0.0.1:{self.mn_port}"],
+        ])
+
+    def run_test(self):
+        masternode: MasternodeInfo = self.mninfo[0]
+        masternode_node = masternode.get_node(self)
+        connector = self.nodes[1]
+        use_v2transport = self.options.v2transport
+
+        expected_addr = f"127.0.0.1:{masternode.nodePort}"
+        alternate_addr = f"127.0.0.1:{self.alt_port}"
+
+        self.wait_until(lambda: masternode_node.masternode("status")["state"] == "READY")
+        assert_equal(masternode_node.masternode("status")["service"], expected_addr)
+
+        self.log.info(f"Connect to the registered masternode service over {'v2' if use_v2transport else 'v1'} and expect MNAUTH")
+        with connector.assert_debug_log([f"Masternode probe successful for {masternode.proTxHash}"]):
+            assert_equal(connector.masternode("connect", expected_addr, use_v2transport), "successfully connected")
+
+        self.log.info(f"Connect to the alternate bind over {'v2' if use_v2transport else 'v1'} and expect no MNAUTH")
+        with masternode_node.assert_debug_log(["Not sending MNAUTH on unexpected local service"]):
+            with connector.assert_debug_log(["connection is a masternode probe but first received message is not MNAUTH"]):
+                assert_equal(connector.masternode("connect", alternate_addr, use_v2transport), "successfully connected")
+
+
+if __name__ == '__main__':
+    P2PMNAUTHTest().main()

test/functional/test_runner.py

@@ -353,6 +353,8 @@
     'p2p_ibd_txrelay.py',
     'rpc_coinjoin.py',
     'rpc_masternode.py',
+    'p2p_mnauth.py --v1transport',
+    'p2p_mnauth.py --v2transport',
     'rpc_mnauth.py',
     'rpc_verifychainlock.py',
     'wallet_create_tx.py --legacy-wallet',