test(cli): add test case for list preservation in merge_json_files

Author: RbBtSn0w

tests/test_merge.py

@@ -120,3 +120,16 @@ def test_merge_json_files_unparseable_existing(tmp_path):
 
     assert merge_json_files(bad_file, {"b": 2}) is None
 
+
+def test_merge_json_files_list_preservation(tmp_path):
+    """Verify that existing list values are preserved and NOT merged or overwritten."""
+    existing_file = tmp_path / "list.json"
+    existing_file.write_text('{"my.list": ["user_item"]}')
+    
+    template_settings = {
+        "my.list": ["template_item"]
+    }
+    
+    merged = merge_json_files(existing_file, template_settings)
+    # The polite merge policy says: keep existing values if they exist and aren't both dicts
+    assert merged["my.list"] == ["user_item"]