Add sensor platform to A. O. Smith integration (#105604)

* Add sensor platform to A. O. Smith integration

* Fix typo

* Remove unnecessary mixin

* Simplify async_setup_entry

tests/components/aosmith/test_sensor.py

@@ -0,0 +1,27 @@
+"""Tests for the sensor platform of the A. O. Smith integration."""
+
+from syrupy.assertion import SnapshotAssertion
+
+from homeassistant.core import HomeAssistant
+from homeassistant.helpers import entity_registry as er
+
+from tests.common import MockConfigEntry
+
+
+async def test_setup(
+    hass: HomeAssistant,
+    entity_registry: er.EntityRegistry,
+    init_integration: MockConfigEntry,
+) -> None:
+    """Test the setup of the sensor entity."""
+    entry = entity_registry.async_get("sensor.my_water_heater_hot_water_availability")
+    assert entry
+    assert entry.unique_id == "hot_water_availability_junctionId"
+
+
+async def test_state(
+    hass: HomeAssistant, init_integration: MockConfigEntry, snapshot: SnapshotAssertion
+) -> None:
+    """Test the state of the sensor entity."""
+    state = hass.states.get("sensor.my_water_heater_hot_water_availability")
+    assert state == snapshot