Add diagnostic to V2C (#118823)

* add diagnostic platform

* add diagnostic platform

* add diagnostic platform

tests/components/v2c/test_diagnostics.py

@@ -0,0 +1,30 @@
+"""Test V2C diagnostics."""
+
+from unittest.mock import AsyncMock
+
+from syrupy import SnapshotAssertion
+
+from homeassistant.config_entries import ConfigEntry
+from homeassistant.core import HomeAssistant
+
+from . import init_integration
+
+from tests.components.diagnostics import get_diagnostics_for_config_entry
+from tests.typing import ClientSessionGenerator
+
+
+async def test_entry_diagnostics(
+    hass: HomeAssistant,
+    mock_config_entry: ConfigEntry,
+    mock_v2c_client: AsyncMock,
+    hass_client: ClientSessionGenerator,
+    snapshot: SnapshotAssertion,
+) -> None:
+    """Test config entry diagnostics."""
+
+    await init_integration(hass, mock_config_entry)
+
+    assert (
+        await get_diagnostics_for_config_entry(hass, hass_client, mock_config_entry)
+        == snapshot()
+    )