Add DHCP discovery subscribe websocket API (#143106)

* Add DHCP discovery subscribe websocket API

* fix circular import

* fixes

* fixes

* fixes

* reduce

* reduce

* reduce

* fix tests

* fix tests

* rework

* tests

* reduce number of lines changed

* reduce

tests/components/dhcp/test_websocket_api.py

@@ -0,0 +1,75 @@
+"""The tests for the dhcp WebSocket API."""
+
+import asyncio
+from collections.abc import Callable
+from unittest.mock import patch
+
+import aiodhcpwatcher
+
+from homeassistant.components.dhcp import DOMAIN
+from homeassistant.core import EVENT_HOMEASSISTANT_STARTED, HomeAssistant
+from homeassistant.setup import async_setup_component
+
+from tests.typing import WebSocketGenerator
+
+
+async def test_subscribe_discovery(
+    hass: HomeAssistant,
+    hass_ws_client: WebSocketGenerator,
+) -> None:
+    """Test dhcp subscribe_discovery."""
+    saved_callback: Callable[[aiodhcpwatcher.DHCPRequest], None] | None = None
+
+    async def mock_start(
+        callback: Callable[[aiodhcpwatcher.DHCPRequest], None],
+    ) -> None:
+        """Mock start."""
+        nonlocal saved_callback
+        saved_callback = callback
+
+    with (
+        patch("homeassistant.components.dhcp.aiodhcpwatcher.async_start", mock_start),
+        patch("homeassistant.components.dhcp.DiscoverHosts"),
+    ):
+        await async_setup_component(hass, DOMAIN, {})
+        await hass.async_block_till_done()
+        hass.bus.async_fire(EVENT_HOMEASSISTANT_STARTED)
+        await hass.async_block_till_done()
+
+    saved_callback(aiodhcpwatcher.DHCPRequest("4.3.2.2", "happy", "44:44:33:11:23:12"))
+    client = await hass_ws_client()
+    await client.send_json(
+        {
+            "id": 1,
+            "type": "dhcp/subscribe_discovery",
+        }
+    )
+    async with asyncio.timeout(1):
+        response = await client.receive_json()
+    assert response["success"]
+
+    async with asyncio.timeout(1):
+        response = await client.receive_json()
+    assert response["event"] == {
+        "add": [
+            {
+                "hostname": "happy",
+                "ip_address": "4.3.2.2",
+                "mac_address": "44:44:33:11:23:12",
+            }
+        ]
+    }
+
+    saved_callback(aiodhcpwatcher.DHCPRequest("4.3.2.1", "sad", "44:44:33:11:23:13"))
+
+    async with asyncio.timeout(1):
+        response = await client.receive_json()
+    assert response["event"] == {
+        "add": [
+            {
+                "hostname": "sad",
+                "ip_address": "4.3.2.1",
+                "mac_address": "44:44:33:11:23:13",
+            }
+        ]
+    }