Add tests mqtt light with single supported color_mode (#91811)

tests/components/mqtt/test_light_json.py

@@ -268,6 +268,49 @@ async def test_fail_setup_if_color_modes_invalid(
     assert error in caplog.text
 
 
+@pytest.mark.parametrize(
+    "hass_config",
+    [
+        {
+            mqtt.DOMAIN: {
+                light.DOMAIN: {
+                    "schema": "json",
+                    "name": "test",
+                    "command_topic": "test_light/set",
+                    "state_topic": "test_light",
+                    "color_mode": True,
+                    "supported_color_modes": "color_temp",
+                }
+            }
+        }
+    ],
+)
+async def test_single_color_mode(
+    hass: HomeAssistant,
+    mqtt_mock_entry: MqttMockHAClientGenerator,
+) -> None:
+    """Test setup with single color_mode."""
+    await mqtt_mock_entry()
+    state = hass.states.get("light.test")
+    assert state.state == STATE_UNKNOWN
+
+    await common.async_turn_on(hass, "light.test", brightness=50, color_temp=192)
+
+    async_fire_mqtt_message(
+        hass,
+        "test_light",
+        '{"state": "ON", "brightness": 50, "color_mode": "color_temp", "color_temp": 192}',
+    )
+    color_modes = [light.ColorMode.COLOR_TEMP]
+    state = hass.states.get("light.test")
+    assert state.state == STATE_ON
+
+    assert state.attributes.get(light.ATTR_SUPPORTED_COLOR_MODES) == color_modes
+    assert state.attributes.get(light.ATTR_COLOR_TEMP) == 192
+    assert state.attributes.get(light.ATTR_BRIGHTNESS) == 50
+    assert state.attributes.get(light.ATTR_COLOR_MODE) == color_modes[0]
+
+
 @pytest.mark.parametrize(
     "hass_config",
     [