Add test for heartbeat command

tests/test_command_heartbeat.py

@@ -0,0 +1,28 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+#
+# @Author: José Sánchez-Gallego ([email protected])
+# @Date: 2024-12-24
+# @Filename: test_command_heartbeat.py
+# @License: BSD 3-clause (http://www.opensource.org/licenses/BSD-3-Clause)
+
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+
+if TYPE_CHECKING:
+    from pytest_mock import MockerFixture
+
+    from lvmecp.actor import ECPActor
+
+
+async def test_command_heartbeat(actor: ECPActor, mocker: MockerFixture):
+    hb_set_mock = mocker.patch.object(actor.plc.modbus["hb_set"], "set")
+
+    cmd = await actor.invoke_mock_command("heartbeat")
+    await cmd
+
+    assert cmd.status.did_succeed
+
+    hb_set_mock.assert_called_once_with(True)