Fix EV sensor unit regression and add coverage (#430)

- Initialize native unit attribute to None to avoid unitless sensor crashes
- Set monetary native unit from HA system currency in async_added_to_hass
- Add regression tests for unitless EV sensors and monetary currency unit

Author: tomer-w

custom_components/victron_mqtt/sensor.py

@@ -104,6 +104,7 @@ def __init__(
         super().__init__(
             device, metric, device_info, "sensor", simple_naming, installation_id
         )
+        self._attr_native_unit_of_measurement = None
         self._attr_device_class = METRIC_TYPE_TO_DEVICE_CLASS.get(metric.metric_type)
         # Enum sensors must not have a state class
         if self._attr_device_class == SensorDeviceClass.ENUM:
@@ -112,19 +113,11 @@ def __init__(
             self._attr_state_class = METRIC_NATURE_TO_STATE_CLASS.get(
                 metric.metric_nature
             )
-        # MONETARY uses hass.config.currency which isn't available in __init__,
-        # so it's handled by the native_unit_of_measurement property instead.
+        # MONETARY uses hass.config.currency which isn't available in __init__.
         if self._attr_device_class != SensorDeviceClass.MONETARY:
             self._set_unit_translation()
         self._attr_native_value = VictronSensor._normalize_value(metric.value)
 
-    @property
-    def native_unit_of_measurement(self) -> str | None:
-        """Return the unit of measurement."""
-        if self._attr_device_class == SensorDeviceClass.MONETARY:
-            return self.hass.config.currency
-        return self._attr_native_unit_of_measurement
-
     @callback
     def _on_update_cb(self, value: Any) -> None:
         if self._baseline is not None:
@@ -142,6 +135,8 @@ def _normalize_value(value: Any) -> Any:
 
     async def async_added_to_hass(self) -> None:
         """Restore persistent state for FormulaMetric energy sensors."""
+        if self._attr_device_class == SensorDeviceClass.MONETARY:
+            self._attr_native_unit_of_measurement = self.hass.config.currency
 
         # Only restore for cumulative FormulaMetric sensors (TOTAL / TOTAL_INCREASING).
         # These metrics start from 0 on each HA restart, so we restore the

tests/test_hub.py

@@ -284,6 +284,51 @@ async def test_sensor(
     assert entities == snapshot
 
 
+async def test_sensor_without_unit_does_not_crash(
+    hass: HomeAssistant,
+    init_integration,
+) -> None:
+    """Test unitless EV sensors are created without native unit errors."""
+    victron_hub, mock_config_entry = init_integration
+
+    await inject_message(victron_hub, "N/123/ev/40/LastEvContact", '{"value": 1780575127}')
+    await finalize_injection(victron_hub)
+    await hass.async_block_till_done()
+
+    entity_registry = er.async_get(hass)
+    entities = er.async_entries_for_config_entry(
+        entity_registry, mock_config_entry.entry_id
+    )
+    assert len(entities) == 1
+
+    state = hass.states.get(entities[0].entity_id)
+    assert state is not None
+    assert state.attributes.get("unit_of_measurement") is None
+
+
+async def test_monetary_sensor_uses_ha_currency(
+    hass: HomeAssistant,
+    init_integration,
+) -> None:
+    """Test EV session cost uses Home Assistant system currency."""
+    victron_hub, mock_config_entry = init_integration
+    hass.config.currency = "EUR"
+
+    await inject_message(victron_hub, "N/123/evcharger/0/Session/Cost", '{"value": 1.23}')
+    await finalize_injection(victron_hub)
+    await hass.async_block_till_done()
+
+    entity_registry = er.async_get(hass)
+    entities = er.async_entries_for_config_entry(
+        entity_registry, mock_config_entry.entry_id
+    )
+    assert len(entities) == 1
+
+    state = hass.states.get(entities[0].entity_id)
+    assert state is not None
+    assert state.attributes.get("unit_of_measurement") == "EUR"
+
+
 async def test_sensor_complex(
     hass: HomeAssistant,
     snapshot: SnapshotAssertion,
@@ -1025,4 +1070,3 @@ async def test_number_with_step(
     assert float(state.state) == 57.6
     assert state.attributes.get("step") == 0.1
 
-