test: expand coverage 64%→76%; add BUGS.md for Gemini migration issues

tests/test_logging_forwarder.py

@@ -0,0 +1,62 @@
+"""
+Tests for decnet.logging.forwarder — parse_log_target, probe_log_target.
+"""
+import socket
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+from decnet.logging.forwarder import parse_log_target, probe_log_target
+
+
+class TestParseLogTarget:
+    def test_valid_ip_port(self):
+        host, port = parse_log_target("192.168.1.5:5140")
+        assert host == "192.168.1.5"
+        assert port == 5140
+
+    def test_valid_hostname_port(self):
+        host, port = parse_log_target("logstash.internal:9600")
+        assert host == "logstash.internal"
+        assert port == 9600
+
+    def test_no_colon_raises(self):
+        with pytest.raises(ValueError, match="Invalid log_target"):
+            parse_log_target("192.168.1.5")
+
+    def test_non_digit_port_raises(self):
+        with pytest.raises(ValueError, match="Invalid log_target"):
+            parse_log_target("192.168.1.5:syslog")
+
+    def test_empty_string_raises(self):
+        with pytest.raises(ValueError):
+            parse_log_target("")
+
+    def test_multiple_colons_uses_last_as_port(self):
+        # IPv6-style or hostname with colons — rsplit takes the last segment
+        host, port = parse_log_target("::1:514")
+        assert port == 514
+
+
+class TestProbeLogTarget:
+    def test_returns_true_when_reachable(self):
+        mock_conn = MagicMock()
+        mock_conn.__enter__ = MagicMock(return_value=mock_conn)
+        mock_conn.__exit__ = MagicMock(return_value=False)
+        with patch("decnet.logging.forwarder.socket.create_connection",
+                   return_value=mock_conn):
+            assert probe_log_target("192.168.1.5:5140") is True
+
+    def test_returns_false_when_connection_refused(self):
+        with patch("decnet.logging.forwarder.socket.create_connection",
+                   side_effect=OSError("Connection refused")):
+            assert probe_log_target("192.168.1.5:5140") is False
+
+    def test_returns_false_on_timeout(self):
+        with patch("decnet.logging.forwarder.socket.create_connection",
+                   side_effect=TimeoutError("timed out")):
+            assert probe_log_target("192.168.1.5:5140") is False
+
+    def test_returns_false_on_invalid_target(self):
+        # ValueError from parse_log_target is caught and returns False
+        assert probe_log_target("not-a-valid-target") is False