ESPHome quality improvements round 2 (#143613)

Co-authored-by: Joost Lekkerkerker <joostlek@outlook.com>

tests/components/esphome/common.py

@@ -0,0 +1,34 @@
+"""ESPHome test common code."""
+
+from homeassistant.components import assist_satellite
+from homeassistant.components.assist_satellite import AssistSatelliteEntity
+
+# pylint: disable-next=hass-component-root-import
+from homeassistant.components.esphome import DOMAIN
+from homeassistant.components.esphome.assist_satellite import EsphomeAssistSatellite
+from homeassistant.const import Platform
+from homeassistant.core import HomeAssistant
+from homeassistant.helpers import entity_registry as er
+from homeassistant.helpers.entity_component import EntityComponent
+
+
+def get_satellite_entity(
+    hass: HomeAssistant, mac_address: str
+) -> EsphomeAssistSatellite | None:
+    """Get the satellite entity for a device."""
+    ent_reg = er.async_get(hass)
+    satellite_entity_id = ent_reg.async_get_entity_id(
+        Platform.ASSIST_SATELLITE, DOMAIN, f"{mac_address}-assist_satellite"
+    )
+    if satellite_entity_id is None:
+        return None
+    assert satellite_entity_id.endswith("_assist_satellite")
+
+    component: EntityComponent[AssistSatelliteEntity] = hass.data[
+        assist_satellite.DOMAIN
+    ]
+    if (entity := component.get_entity(satellite_entity_id)) is not None:
+        assert isinstance(entity, EsphomeAssistSatellite)
+        return entity
+
+    return None