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

tests/components/mqtt/test_light_template.py

@@ -183,6 +183,45 @@ async def test_rgb_light(
     assert state.attributes.get(ATTR_SUPPORTED_FEATURES) == expected_features
 
 
+@pytest.mark.parametrize(
+    "hass_config",
+    [
+        {
+            mqtt.DOMAIN: {
+                light.DOMAIN: {
+                    "schema": "template",
+                    "name": "test",
+                    "command_topic": "test_light/set",
+                    "command_on_template": "on,{{ brightness|d }},{{ color_temp|d }}",
+                    "command_off_template": "off",
+                    "brightness_template": "{{ value.split(',')[1] }}",
+                    "color_temp_template": "{{ value.split(',')[2] }}",
+                }
+            }
+        }
+    ],
+)
+async def test_single_color_mode(
+    hass: HomeAssistant, mqtt_mock_entry: MqttMockHAClientGenerator
+) -> None:
+    """Test the color mode when we only have one supported 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", "on,50,192")
+    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",
     [