[API] Sub devices and areas (#8544)

Co-authored-by: J. Nick Koston <nick@koston.org>
Co-authored-by: Jesse Hills <3060199+jesserockz@users.noreply.github.com>
Co-authored-by: J. Nick Koston <nick+github@koston.org>

tests/unit_tests/core/common.py

@@ -0,0 +1,33 @@
+"""Common test utilities for core unit tests."""
+
+from collections.abc import Callable
+from pathlib import Path
+from unittest.mock import patch
+
+from esphome import config, yaml_util
+from esphome.config import Config
+from esphome.core import CORE
+
+
+def load_config_from_yaml(
+    yaml_file: Callable[[str], str], yaml_content: str
+) -> Config | None:
+    """Load configuration from YAML content."""
+    yaml_path = yaml_file(yaml_content)
+    parsed_yaml = yaml_util.load_yaml(yaml_path)
+
+    # Mock yaml_util.load_yaml to return our parsed content
+    with (
+        patch.object(yaml_util, "load_yaml", return_value=parsed_yaml),
+        patch.object(CORE, "config_path", yaml_path),
+    ):
+        return config.read_config({})
+
+
+def load_config_from_fixture(
+    yaml_file: Callable[[str], str], fixture_name: str, fixtures_dir: Path
+) -> Config | None:
+    """Load configuration from a fixture file."""
+    fixture_path = fixtures_dir / fixture_name
+    yaml_content = fixture_path.read_text()
+    return load_config_from_yaml(yaml_file, yaml_content)