From 99e1a7a676b2fc14f9f8a8db64bee2840fae4646 Mon Sep 17 00:00:00 2001
From: Jan Bouwhuis <jbouwh@users.noreply.github.com>
Date: Thu, 6 Mar 2025 18:52:46 +0100
Subject: [PATCH] Check if the unit of measurement is valid before creating the
 entity (#139932)

---
 homeassistant/components/mqtt/sensor.py | 15 ++++++++++++++
 tests/components/mqtt/test_sensor.py    | 26 +++++++++++++++++++++++++
 2 files changed, 41 insertions(+)

diff --git a/homeassistant/components/mqtt/sensor.py b/homeassistant/components/mqtt/sensor.py
index 3e8a4fef0fa..432431c96d9 100644
--- a/homeassistant/components/mqtt/sensor.py
+++ b/homeassistant/components/mqtt/sensor.py
@@ -11,6 +11,7 @@ import voluptuous as vol
 from homeassistant.components import sensor
 from homeassistant.components.sensor import (
     CONF_STATE_CLASS,
+    DEVICE_CLASS_UNITS,
     DEVICE_CLASSES_SCHEMA,
     ENTITY_ID_FORMAT,
     STATE_CLASSES_SCHEMA,
@@ -107,6 +108,20 @@ def validate_sensor_state_and_device_class_config(config: ConfigType) -> ConfigT
                 f"got `{CONF_DEVICE_CLASS}` '{device_class}'"
             )
 
+    if (device_class := config.get(CONF_DEVICE_CLASS)) is None or (
+        unit_of_measurement := config.get(CONF_UNIT_OF_MEASUREMENT)
+    ) is None:
+        return config
+
+    if (
+        device_class in DEVICE_CLASS_UNITS
+        and unit_of_measurement not in DEVICE_CLASS_UNITS[device_class]
+    ):
+        raise vol.Invalid(
+            f"The unit of measurement `{unit_of_measurement}` is not valid "
+            f"together with device class `{device_class}`"
+        )
+
     return config
 
 
diff --git a/tests/components/mqtt/test_sensor.py b/tests/components/mqtt/test_sensor.py
index 9226b03a7d2..f40082d84be 100644
--- a/tests/components/mqtt/test_sensor.py
+++ b/tests/components/mqtt/test_sensor.py
@@ -870,6 +870,32 @@ async def test_invalid_device_class(
     assert "expected SensorDeviceClass or one of" in caplog.text
 
 
+@pytest.mark.parametrize(
+    "hass_config",
+    [
+        {
+            mqtt.DOMAIN: {
+                sensor.DOMAIN: {
+                    "name": "test",
+                    "state_topic": "test-topic",
+                    "device_class": "energy",
+                    "unit_of_measurement": "ppm",
+                }
+            }
+        }
+    ],
+)
+async def test_invalid_unit_of_measurement(
+    mqtt_mock_entry: MqttMockHAClientGenerator, caplog: pytest.LogCaptureFixture
+) -> None:
+    """Test device_class with invalid unit of measurement."""
+    assert await mqtt_mock_entry()
+    assert (
+        "The unit of measurement `ppm` is not valid together with device class `energy`"
+        in caplog.text
+    )
+
+
 @pytest.mark.parametrize(
     "hass_config",
     [