[config_validation] extend should combine extra validations (#9939)

tests/component_tests/config_validation/test_config.py

@@ -0,0 +1,51 @@
+"""
+Test schema.extend functionality in esphome.config_validation.
+"""
+
+from typing import Any
+
+import esphome.config_validation as cv
+
+
+def test_config_extend() -> None:
+    """Test that schema.extend correctly merges schemas with extras."""
+
+    def func1(data: dict[str, Any]) -> dict[str, Any]:
+        data["extra_1"] = "value1"
+        return data
+
+    def func2(data: dict[str, Any]) -> dict[str, Any]:
+        data["extra_2"] = "value2"
+        return data
+
+    schema1 = cv.Schema(
+        {
+            cv.Required("key1"): cv.string,
+        }
+    )
+    schema1.add_extra(func1)
+    schema2 = cv.Schema(
+        {
+            cv.Required("key2"): cv.string,
+        }
+    )
+    schema2.add_extra(func2)
+    extended_schema = schema1.extend(schema2)
+    config = {
+        "key1": "initial_value1",
+        "key2": "initial_value2",
+    }
+    validated = extended_schema(config)
+    assert validated["key1"] == "initial_value1"
+    assert validated["key2"] == "initial_value2"
+    assert validated["extra_1"] == "value1"
+    assert validated["extra_2"] == "value2"
+
+    # Check the opposite order of extension
+    extended_schema = schema2.extend(schema1)
+
+    validated = extended_schema(config)
+    assert validated["key1"] == "initial_value1"
+    assert validated["key2"] == "initial_value2"
+    assert validated["extra_1"] == "value1"
+    assert validated["extra_2"] == "value2"