diff --git a/tests/test_firewall_sync.py b/tests/test_firewall_sync.py
new file mode 100644
index 0000000..998d15c
--- /dev/null
+++ b/tests/test_firewall_sync.py
@@ -0,0 +1,65 @@
+#!/usr/bin/env python3
+"""Tests for evidence-first firewall sync behavior."""
+
+from __future__ import annotations
+
+import unittest
+from unittest.mock import patch
+
+from app.firewall import MikrotikFirewall
+
+
+class _FakeFirewall(MikrotikFirewall):
+    def __init__(self):
+        super().__init__(router_ip="0.0.0.0", username="x", password="x")
+        self.calls: list[str] = []
+
+    def get_address_list_ipv4(self, name: str) -> set[str]:
+        self.calls.append(f"v4:{name}")
+        if name == "Blocked":
+            return {"9.9.9.9/32"}
+        if name == "Init7":
+            return {"77.74.80.0/21"}
+        return set()
+
+    def get_address_list_ipv6(self, name: str) -> set[str]:
+        self.calls.append(f"v6:{name}")
+        if name == "Blocked":
+            return set()
+        if name == "Init7":
+            return {"2001:1620::/30"}
+        return set()
+
+
+class FirewallSyncEvidenceTest(unittest.TestCase):
+    def test_sync_loads_router_status_before_computing_changes(self):
+        fw = _FakeFirewall()
+        # type: ignore[assignment]
+        fw.save_state_report = lambda *args, **kwargs: "noop"
+
+        with patch("app.firewall.cumulative_blocklist",
+                   return_value=({"8.8.8.8/32"}, set())):
+            changes = fw.sync_blocklist(["8.8.8.8/32"], [], dry_run=True)
+
+        self.assertIn("v4:Blocked", fw.calls)
+        self.assertIn("v6:Blocked", fw.calls)
+        self.assertIn("v4:Init7", fw.calls)
+        self.assertIn("v6:Init7", fw.calls)
+        self.assertEqual(changes["added_ipv4"], ["8.8.8.8/32"])
+        self.assertEqual(changes["removed_ipv4"], ["9.9.9.9/32"])
+
+    def test_sync_evaluates_against_loaded_current_status(self):
+        fw = _FakeFirewall()
+        # type: ignore[assignment]
+        fw.save_state_report = lambda *args, **kwargs: "noop"
+
+        with patch("app.firewall.cumulative_blocklist",
+                   return_value=({"9.9.9.9/32"}, set())):
+            changes = fw.sync_blocklist(["9.9.9.9/32"], [], dry_run=True)
+
+        self.assertEqual(changes["added_ipv4"], [])
+        self.assertEqual(changes["removed_ipv4"], [])
+
+
+if __name__ == "__main__":
+    unittest.main()