Always update unit of measurement of the utility_meter on state change

homeassistant/components/utility_meter/sensor.py

@@ -17,6 +17,7 @@
     SensorExtraStoredData,
     SensorStateClass,
 )
+from homeassistant.components.sensor.recorder import _suggest_report_issue
 from homeassistant.config_entries import ConfigEntry
 from homeassistant.const import (
     ATTR_UNIT_OF_MEASUREMENT,
@@ -484,13 +485,20 @@ def async_reading(self, event: EventType[EventStateChangedData]) -> None:
                 DATA_TARIFF_SENSORS
             ]:
                 sensor.start(new_state.attributes.get(ATTR_UNIT_OF_MEASUREMENT))
+                if self._unit_of_measurement is None:
+                    _LOGGER.warning(
+                        "Source sensor %s has no unit of measurement. Please %s",
+                        self._sensor_source_id,
+                        _suggest_report_issue(self.hass, self._sensor_source_id),
+                    )
 
         if (
             adjustment := self.calculate_adjustment(old_state, new_state)
         ) is not None and (self._sensor_net_consumption or adjustment >= 0):
             # If net_consumption is off, the adjustment must be non-negative
             self._state += adjustment  # type: ignore[operator] # self._state will be set to by the start function if it is None, therefore it always has a valid Decimal value at this line
 
+        self._unit_of_measurement = new_state.attributes.get(ATTR_UNIT_OF_MEASUREMENT)
         self._last_valid_state = new_state_val
         self.async_write_ha_state()
 

tests/components/utility_meter/test_sensor.py

@@ -1460,6 +1460,39 @@ def test_calculate_adjustment_invalid_new_state(
     assert "Invalid state unknown" in caplog.text
 
 
+async def test_unit_of_measurement_missing_invalid_new_state(
+    hass: HomeAssistant,
+    caplog: pytest.LogCaptureFixture,
+) -> None:
+    """Test that a suggestion is created when new_state is missing unit_of_measurement."""
+    yaml_config = {
+        "utility_meter": {
+            "energy_bill": {
+                "source": "sensor.energy",
+            }
+        }
+    }
+    source_entity_id = yaml_config[DOMAIN]["energy_bill"]["source"]
+
+    assert await async_setup_component(hass, DOMAIN, yaml_config)
+    await hass.async_block_till_done()
+
+    hass.bus.async_fire(EVENT_HOMEASSISTANT_STARTED)
+    await hass.async_block_till_done()
+
+    hass.states.async_set(source_entity_id, 4, {ATTR_UNIT_OF_MEASUREMENT: None})
+
+    await hass.async_block_till_done()
+
+    state = hass.states.get("sensor.energy_bill")
+    assert state is not None
+    assert state.state == "0"
+    assert state.attributes.get(ATTR_UNIT_OF_MEASUREMENT) is None
+    assert (
+        f"Source sensor {source_entity_id} has no unit of measurement." in caplog.text
+    )
+
+
 async def test_device_id(hass: HomeAssistant) -> None:
     """Test for source entity device for Utility Meter."""
     device_registry = dr.async_get(hass)