Track availability of source sensor in utility meter (#91035)

* track availability of source sensor

* address review comments

homeassistant/components/utility_meter/sensor.py

@@ -423,6 +423,15 @@ class UtilityMeterSensor(RestoreSensor):
     @callback
     def async_reading(self, event: Event):
         """Handle the sensor state changes."""
+        if (
+            source_state := self.hass.states.get(self._sensor_source_id)
+        ) is None or source_state.state == STATE_UNAVAILABLE:
+            self._attr_available = False
+            self.async_write_ha_state()
+            return
+
+        self._attr_available = True
+
         old_state: State | None = event.data.get("old_state")
         new_state: State = event.data.get("new_state")  # type: ignore[assignment] # a state change event always has a new state
 

tests/components/utility_meter/test_sensor.py

@@ -217,20 +217,19 @@ async def test_state(hass: HomeAssistant, yaml_config, config_entry_config) -> N
         entity_id, "*", {ATTR_UNIT_OF_MEASUREMENT: UnitOfEnergy.KILO_WATT_HOUR}
     )
     await hass.async_block_till_done()
-    state = hass.states.get("sensor.energy_bill_midpeak")
+    state = hass.states.get("sensor.energy_bill_offpeak")
     assert state is not None
-    assert state.state == "0.123"
+    assert state.state == "3"
 
     # test unavailable source
     hass.states.async_set(
         entity_id,
         STATE_UNAVAILABLE,
-        {ATTR_UNIT_OF_MEASUREMENT: UnitOfEnergy.KILO_WATT_HOUR},
     )
     await hass.async_block_till_done()
-    state = hass.states.get("sensor.energy_bill_midpeak")
+    state = hass.states.get("sensor.energy_bill_offpeak")
     assert state is not None
-    assert state.state == "0.123"
+    assert state.state == "unavailable"
 
 
 @pytest.mark.parametrize(