Bring modbus back to 100% test coverage (home-assistant#85972)

Co-authored-by: epenet <6771947+epenet@users.noreply.github.com>

tests/components/modbus/test_init.py

@@ -862,3 +862,20 @@ async def test_integration_reload(
             async_fire_time_changed(hass)
             await hass.async_block_till_done()
     assert "Modbus reloading" in caplog.text
+
+
+@pytest.mark.parametrize("do_config", [{}])
+async def test_integration_reload_failed(hass, caplog, mock_modbus) -> None:
+    """Run test for integration connect failure on reload."""
+    caplog.set_level(logging.INFO)
+    caplog.clear()
+
+    yaml_path = get_fixture_path("configuration.yaml", "modbus")
+    with mock.patch.object(
+        hass_config, "YAML_CONFIG_FILE", yaml_path
+    ), mock.patch.object(mock_modbus, "connect", side_effect=ModbusException("error")):
+        await hass.services.async_call(DOMAIN, SERVICE_RELOAD, blocking=True)
+        await hass.async_block_till_done()
+
+    assert "Modbus reloading" in caplog.text
+    assert "connect failed, retry in pymodbus" in caplog.text