Fix cpu percentage in System Monitor (#110268)

* Fix cpu percentage in System Monitor

* Tests

homeassistant/components/systemmonitor/coordinator.py

@@ -1,4 +1,5 @@
 """DataUpdateCoordinators for the System monitor integration."""
+
 from __future__ import annotations
 
 from abc import abstractmethod
@@ -43,7 +44,8 @@ dataT = TypeVar(
     | sswap
     | VirtualMemory
     | tuple[float, float, float]
-    | sdiskusage,
+    | sdiskusage
+    | None,
 )
 
 
@@ -130,12 +132,15 @@ class SystemMonitorLoadCoordinator(MonitorCoordinator[tuple[float, float, float]
         return os.getloadavg()
 
 
-class SystemMonitorProcessorCoordinator(MonitorCoordinator[float]):
+class SystemMonitorProcessorCoordinator(MonitorCoordinator[float | None]):
     """A System monitor Processor Data Update Coordinator."""
 
-    def update_data(self) -> float:
+    def update_data(self) -> float | None:
         """Fetch data."""
-        return psutil.cpu_percent(interval=None)
+        cpu_percent = psutil.cpu_percent(interval=None)
+        if cpu_percent > 0.0:
+            return cpu_percent
+        return None
 
 
 class SystemMonitorBootTimeCoordinator(MonitorCoordinator[datetime]):

homeassistant/components/systemmonitor/sensor.py

@@ -346,7 +346,9 @@ SENSOR_TYPES: dict[str, SysMonitorSensorEntityDescription[Any]] = {
         native_unit_of_measurement=PERCENTAGE,
         icon=get_cpu_icon(),
         state_class=SensorStateClass.MEASUREMENT,
-        value_fn=lambda entity: round(entity.coordinator.data),
+        value_fn=lambda entity: (
+            round(entity.coordinator.data) if entity.coordinator.data else None
+        ),
     ),
     "processor_temperature": SysMonitorSensorEntityDescription[
         dict[str, list[shwtemp]]

tests/components/systemmonitor/test_sensor.py

@@ -1,4 +1,5 @@
 """Test System Monitor sensor."""
+
 from datetime import timedelta
 import socket
 from unittest.mock import Mock, patch
@@ -529,3 +530,37 @@ async def test_exception_handling_disk_sensor(
     assert disk_sensor is not None
     assert disk_sensor.state == "70.0"
     assert disk_sensor.attributes["unit_of_measurement"] == "%"
+
+
+async def test_cpu_percentage_is_zero_returns_unknown(
+    hass: HomeAssistant,
+    entity_registry_enabled_by_default: None,
+    mock_psutil: Mock,
+    mock_added_config_entry: ConfigEntry,
+    caplog: pytest.LogCaptureFixture,
+    freezer: FrozenDateTimeFactory,
+) -> None:
+    """Test the sensor."""
+    cpu_sensor = hass.states.get("sensor.system_monitor_processor_use")
+    assert cpu_sensor is not None
+    assert cpu_sensor.state == "10"
+
+    mock_psutil.cpu_percent.return_value = 0.0
+
+    freezer.tick(timedelta(minutes=1))
+    async_fire_time_changed(hass)
+    await hass.async_block_till_done()
+
+    cpu_sensor = hass.states.get("sensor.system_monitor_processor_use")
+    assert cpu_sensor is not None
+    assert cpu_sensor.state == STATE_UNKNOWN
+
+    mock_psutil.cpu_percent.return_value = 15.0
+
+    freezer.tick(timedelta(minutes=1))
+    async_fire_time_changed(hass)
+    await hass.async_block_till_done()
+
+    cpu_sensor = hass.states.get("sensor.system_monitor_processor_use")
+    assert cpu_sensor is not None
+    assert cpu_sensor.state == "15"