test(ci): cover assurance gate entry points

tests/unit/test_docker_host_address.py

@@ -3,8 +3,11 @@
 from __future__ import annotations
 
 import unittest
+from contextlib import redirect_stderr, redirect_stdout
+from io import StringIO
+from unittest.mock import patch
 
-from scripts.docker_host_address import default_ipv4_gateway
+from scripts.docker_host_address import default_ipv4_gateway, main
 
 
 class TestDefaultIpv4Gateway(unittest.TestCase):
@@ -23,6 +26,34 @@ class TestDefaultIpv4Gateway(unittest.TestCase):
         with self.assertRaisesRegex(ValueError, "no active"):
             default_ipv4_gateway(routes)
 
+    def test_ignores_short_malformed_and_inactive_routes(self) -> None:
+        routes = (
+            "Iface Destination Gateway Flags\n"
+            "short row\n"
+            "eth0 00000000 nope 0003\n"
+            "eth0 00000000 010011AC 0001\n"
+        )
+        with self.assertRaisesRegex(ValueError, "no active"):
+            default_ipv4_gateway(routes)
+
+    def test_main_prints_gateway(self) -> None:
+        routes = (
+            "Iface Destination Gateway Flags\n"
+            "eth0 00000000 010011AC 0003\n"
+        )
+        output = StringIO()
+        with patch("pathlib.Path.read_text", return_value=routes), \
+                redirect_stdout(output):
+            self.assertEqual(0, main())
+        self.assertEqual("172.17.0.1\n", output.getvalue())
+
+    def test_main_reports_route_error(self) -> None:
+        error = StringIO()
+        with patch("pathlib.Path.read_text", side_effect=OSError("denied")), \
+                redirect_stderr(error):
+            self.assertEqual(1, main())
+        self.assertIn("docker-host-address: denied", error.getvalue())
+
 
 if __name__ == "__main__":
     unittest.main()