Correct calls to subscription.async_unsubscribe_topics (#19414)

* Correct calls to subscription.async_unsubscribe_topics

* Review comments

* Add testcases

tests/components/sensor/test_mqtt.py

@@ -3,7 +3,7 @@ import json
 import unittest
 
 from datetime import timedelta, datetime
-from unittest.mock import patch
+from unittest.mock import ANY, patch
 
 import homeassistant.core as ha
 from homeassistant.setup import setup_component, async_setup_component
@@ -15,7 +15,7 @@ import homeassistant.util.dt as dt_util
 
 from tests.common import mock_mqtt_component, fire_mqtt_message, \
     assert_setup_component, async_fire_mqtt_message, \
-    async_mock_mqtt_component, MockConfigEntry
+    async_mock_mqtt_component, MockConfigEntry, mock_registry
 from tests.common import get_test_home_assistant, mock_component
 
 
@@ -542,3 +542,38 @@ async def test_entity_device_info_with_identifier(hass, mqtt_mock):
     assert device.name == 'Beer'
     assert device.model == 'Glass'
     assert device.sw_version == '0.1-beta'
+
+
+async def test_entity_id_update(hass, mqtt_mock):
+    """Test MQTT subscriptions are managed when entity_id is updated."""
+    registry = mock_registry(hass, {})
+    mock_mqtt = await async_mock_mqtt_component(hass)
+    assert await async_setup_component(hass, sensor.DOMAIN, {
+        sensor.DOMAIN: [{
+            'platform': 'mqtt',
+            'name': 'beer',
+            'state_topic': 'test-topic',
+            'availability_topic': 'avty-topic',
+            'unique_id': 'TOTALLY_UNIQUE'
+        }]
+    })
+
+    state = hass.states.get('sensor.beer')
+    assert state is not None
+    assert mock_mqtt.async_subscribe.call_count == 2
+    mock_mqtt.async_subscribe.assert_any_call('test-topic', ANY, 0, 'utf-8')
+    mock_mqtt.async_subscribe.assert_any_call('avty-topic', ANY, 0, 'utf-8')
+    mock_mqtt.async_subscribe.reset_mock()
+
+    registry.async_update_entity('sensor.beer', new_entity_id='sensor.milk')
+    await hass.async_block_till_done()
+    await hass.async_block_till_done()
+
+    state = hass.states.get('sensor.beer')
+    assert state is None
+
+    state = hass.states.get('sensor.milk')
+    assert state is not None
+    assert mock_mqtt.async_subscribe.call_count == 2
+    mock_mqtt.async_subscribe.assert_any_call('test-topic', ANY, 0, 'utf-8')
+    mock_mqtt.async_subscribe.assert_any_call('avty-topic', ANY, 0, 'utf-8')