fix: raise when async_set_low_voltage_state has no mode to send

If neither the mode argument nor the device's reported mode was
available, Thermostat24VMode silently dropped out of the payload
(filtered as None) and the request sent only the setpoints -- exactly
the partial write this method exists to prevent. Raise ValueError
instead of sending it.

Also tighten payload's type from dict[str, Any] to
dict[str, str | int | float | None], mirroring
HiloDevice.set_attributes()'s own signature.

Author: ColtHub

pyhilo/device/climate.py

@@ -216,9 +216,21 @@ async def async_set_low_voltage_state(
         have to be sent in one request even when only one of them changed.
         Arguments left out keep their current value; values the device does
         not report at all are omitted from the payload.
-        """
-        payload: dict[str, Any] = {
-            "Thermostat24VMode": mode if mode is not None else self.low_voltage_mode,
+
+        Raises:
+            ValueError: The mode isn't given and the device hasn't reported
+                one either. Silently dropping Thermostat24VMode from the
+                payload in that case would send setpoints without a mode,
+                exactly the partial write this method exists to prevent.
+        """
+        resolved_mode = mode if mode is not None else self.low_voltage_mode
+        if resolved_mode is None:
+            raise ValueError(
+                f"{self._tag} Cannot set low voltage state: no mode was given "
+                "and the device has not reported one. Pass mode explicitly."
+            )
+        payload: dict[str, str | int | float | None] = {
+            "Thermostat24VMode": resolved_mode,
             "TargetTemperature": (
                 target_temperature
                 if target_temperature is not None

tests/test_climate.py

@@ -1,5 +1,7 @@
 from unittest.mock import AsyncMock, MagicMock
 
+import pytest
+
 from pyhilo.const import HILO_READING_TYPES, STATE_UNKNOWN
 from pyhilo.device import DeviceAttribute, DeviceReading, get_device_attributes
 from pyhilo.device.climate import Climate, as_list
@@ -182,3 +184,13 @@ async def test_absent_values_are_not_sent(self):
         device.set_attributes.assert_awaited_once_with(
             {"Thermostat24VMode": "HEAT", "TargetTemperature": 22}
         )
+
+    async def test_unreported_mode_without_explicit_mode_raises(self):
+        """A device that hasn't reported Thermostat24VMode can't be written to
+        without an explicit mode: silently dropping the key would send only
+        the setpoints, the exact partial write this method must prevent."""
+        device = _climate(TargetTemperature=19, CoolTemperatureSet=24)
+        device.set_attributes = AsyncMock()
+        with pytest.raises(ValueError):
+            await device.async_set_low_voltage_state(cool_setpoint=22)
+        device.set_attributes.assert_not_awaited()