refactor(filter_plugins/url_join): enforce mandatory scheme and raise specific AnsibleFilterError messages

Improved url_join filter:
- Requires first element to contain a valid '<scheme>://'
- Raises specific errors for None, empty list, wrong type, missing scheme,
  extra schemes in later parts, or string conversion failures
- Provides clearer error messages with index context in parts

See: https://chatgpt.com/share/68b537ea-d198-800f-927a-940c4de832f2

tests/unit/filter_plugins/test_url_join.py

@@ -0,0 +1,100 @@
+import unittest
+import sys
+import os
+
+# Ensure filter_plugins directory is on the path
+sys.path.insert(
+    0,
+    os.path.abspath(os.path.join(os.path.dirname(__file__), '../../../filter_plugins'))
+)
+
+from ansible.errors import AnsibleFilterError
+from url_join import url_join
+
+
+class TestUrlJoinFilter(unittest.TestCase):
+    # --- success cases ---
+    def test_http_basic(self):
+        self.assertEqual(
+            url_join(['http://example.com', 'foo', 'bar']),
+            'http://example.com/foo/bar'
+        )
+
+    def test_https_slashes(self):
+        self.assertEqual(
+            url_join(['https://example.com/', '/api/', '/v1/', '/users/']),
+            'https://example.com/api/v1/users'
+        )
+
+    def test_custom_scheme(self):
+        self.assertEqual(
+            url_join(['myapp+v1://host/', '//section', 'item']),
+            'myapp+v1://host/section/item'
+        )
+
+    def test_scheme_with_path_in_first(self):
+        self.assertEqual(
+            url_join(['https://example.com/base/', '/deep/', 'leaf']),
+            'https://example.com/base/deep/leaf'
+        )
+
+    def test_none_in_list(self):
+        self.assertEqual(
+            url_join(['https://example.com', None, 'foo']),
+            'https://example.com/foo'
+        )
+
+    def test_numeric_parts(self):
+        self.assertEqual(
+            url_join(['https://example.com', 123, '456']),
+            'https://example.com/123/456'
+        )
+
+    def test_only_scheme_returns_scheme(self):
+        self.assertEqual(
+            url_join(['https://']),
+            'https://'
+        )
+
+    # --- error cases with specific messages ---
+    def test_none_input_raises(self):
+        with self.assertRaisesRegex(AnsibleFilterError, r"parts must be a non-empty list; got None"):
+            url_join(None)
+
+    def test_empty_list_raises(self):
+        with self.assertRaisesRegex(AnsibleFilterError, r"parts must be a non-empty list"):
+            url_join([])
+
+    def test_non_list_raises(self):
+        with self.assertRaisesRegex(AnsibleFilterError, r"parts must be a list/tuple; got str"):
+            url_join("https://example.com")
+
+    def test_first_none_raises(self):
+        with self.assertRaisesRegex(AnsibleFilterError, r"first element must include a scheme"):
+            url_join([None, 'foo'])
+
+    def test_no_scheme_raises(self):
+        with self.assertRaisesRegex(AnsibleFilterError, r"must start with '<scheme>://'"):
+            url_join(['example.com', 'foo'])
+
+    def test_additional_scheme_in_later_part_raises(self):
+        with self.assertRaisesRegex(AnsibleFilterError, r"only the first element may contain a scheme"):
+            url_join(['https://example.com', 'https://elsewhere'])
+
+    def test_unstringifiable_first_part_raises(self):
+        class Bad:
+            def __str__(self):
+                raise ValueError("boom")
+        with self.assertRaisesRegex(AnsibleFilterError, r"unable to convert part at index 0"):
+            url_join([Bad(), 'x'])
+
+    def test_unstringifiable_later_part_raises(self):
+        class Bad:
+            def __str__(self):
+                raise ValueError("boom")
+        with self.assertRaisesRegex(AnsibleFilterError, r"unable to convert part at index 2"):
+            url_join(['https://example.com', 'ok', Bad()])
+
+
+if __name__ == '__main__':
+    unittest.main()