Add MQTT debug info (#33461)

* Add MQTT debug info

* Tweaks

* Tweaks

tests/components/mqtt/test_init.py

@@ -1,5 +1,6 @@
 """The tests for the MQTT component."""
 from datetime import timedelta
+import json
 import ssl
 import unittest
 from unittest import mock
@@ -934,3 +935,48 @@ async def test_mqtt_ws_remove_non_mqtt_device(
     response = await client.receive_json()
     assert not response["success"]
     assert response["error"]["code"] == websocket_api.const.ERR_NOT_FOUND
+
+
+async def test_mqtt_ws_get_device_debug_info(
+    hass, device_reg, hass_ws_client, mqtt_mock
+):
+    """Test MQTT websocket device debug info."""
+    config_entry = MockConfigEntry(domain=mqtt.DOMAIN)
+    config_entry.add_to_hass(hass)
+    await async_start(hass, "homeassistant", {}, config_entry)
+
+    config = {
+        "device": {"identifiers": ["0AFFD2"]},
+        "platform": "mqtt",
+        "state_topic": "foobar/sensor",
+        "unique_id": "unique",
+    }
+    data = json.dumps(config)
+
+    async_fire_mqtt_message(hass, "homeassistant/sensor/bla/config", data)
+    await hass.async_block_till_done()
+
+    # Verify device entry is created
+    device_entry = device_reg.async_get_device({("mqtt", "0AFFD2")}, set())
+    assert device_entry is not None
+
+    client = await hass_ws_client(hass)
+    await client.send_json(
+        {"id": 5, "type": "mqtt/device/debug_info", "device_id": device_entry.id}
+    )
+    response = await client.receive_json()
+    assert response["success"]
+    expected_result = {
+        "entities": [
+            {
+                "entity_id": "sensor.mqtt_sensor",
+                "topics": [{"topic": "foobar/sensor", "messages": []}],
+                "discovery_data": {
+                    "payload": config,
+                    "topic": "homeassistant/sensor/bla/config",
+                },
+            }
+        ],
+        "triggers": [],
+    }
+    assert response["result"] == expected_result