Solved bug existed due to difference between mailu domain and hostname difference. also refactored during this to find the bug

tests/unit/filter_plugins/test_domain_tools.py

@@ -0,0 +1,49 @@
+import os
+import sys
+import unittest
+
+# Make project root importable so "filter_plugins.domain_tools" works no matter where tests run from
+THIS_DIR = os.path.dirname(os.path.abspath(__file__))
+PROJECT_ROOT = os.path.abspath(os.path.join(THIS_DIR, '..', '..', '..'))
+if PROJECT_ROOT not in sys.path:
+    sys.path.insert(0, PROJECT_ROOT)
+
+from ansible.errors import AnsibleFilterError  # noqa: E402
+from filter_plugins.domain_tools import to_zone, FilterModule  # noqa: E402
+
+
+class TestDomainTools(unittest.TestCase):
+    def test_to_zone_basic(self):
+        self.assertEqual(to_zone("example.com"), "example.com")
+        self.assertEqual(to_zone("mail.example.com"), "example.com")
+        self.assertEqual(to_zone("a.b.c.example.com"), "example.com")
+
+    def test_to_zone_trailing_and_leading_dots(self):
+        self.assertEqual(to_zone("example.com."), "example.com")
+        self.assertEqual(to_zone(".mail.example.com."), "example.com")
+
+    def test_to_zone_keeps_two_last_labels(self):
+        # Naive behavior by design: last two labels only
+        self.assertEqual(to_zone("service.co.uk"), "co.uk")
+        self.assertEqual(to_zone("mx.mail.service.co.uk"), "co.uk")
+        self.assertEqual(to_zone("uni.edu.pl"), "edu.pl")
+
+    def test_to_zone_invalid_inputs(self):
+        with self.assertRaises(AnsibleFilterError):
+            to_zone("")  # empty
+        with self.assertRaises(AnsibleFilterError):
+            to_zone("   ")  # whitespace
+        with self.assertRaises(AnsibleFilterError):
+            to_zone("localhost")  # no TLD part
+        with self.assertRaises(AnsibleFilterError):
+            to_zone(None)  # type: ignore
+
+    def test_filtermodule_exports(self):
+        fm = FilterModule()
+        filters = fm.filters()
+        self.assertIn("to_zone", filters)
+        self.assertIs(filters["to_zone"], to_zone)
+
+
+if __name__ == "__main__":
+    unittest.main()