feat: add tests for known hosts management and enhance validation in known_hosts.py

tests/test_config.py

@@ -2,6 +2,7 @@ from __future__ import annotations
 
 import os
 import unittest
+from pathlib import Path
 from types import SimpleNamespace
 from unittest.mock import patch
 
@@ -68,3 +69,22 @@ class ArchitectureSettingsTests(unittest.TestCase):
             self.assertRaisesRegex(ConfigurationError, "unsupported host architecture: riscv64"),
         ):
             Settings.from_environment()
+
+
+class KnownHostsSettingsTests(unittest.TestCase):
+    def test_known_hosts_files_are_loaded_as_explicit_absolute_paths(self) -> None:
+        with patch.dict(os.environ, {
+            "UVM_KNOWN_HOSTS_FILES": "/root/.ssh/known_hosts:/home/operator/.ssh/known_hosts",
+        }, clear=True):
+            settings = Settings.from_environment()
+        self.assertEqual(settings.known_hosts_files, (
+            Path("/root/.ssh/known_hosts"), Path("/home/operator/.ssh/known_hosts"),
+        ))
+        with patch.dict(os.environ, {}, clear=True):
+            self.assertIsNone(Settings.from_environment().known_hosts_files)
+
+    def test_relative_or_empty_path_entries_are_rejected(self) -> None:
+        for value in ("known_hosts", "/tmp/known_hosts:", ":/tmp/known_hosts"):
+            with self.subTest(value=value), patch.dict(os.environ, {"UVM_KNOWN_HOSTS_FILES": value}, clear=True):
+                with self.assertRaisesRegex(ConfigurationError, "UVM_KNOWN_HOSTS_FILES"):
+                    Settings.from_environment()