Fix missing line to Add tests for launch_utils of controller manager (ros-controls#2147)

Author: robkwan

controller_manager/test/test_ros2_control_node_launch.py

@@ -37,6 +37,7 @@
 from launch_testing.actions import ReadyToTest
 import launch_testing.markers
 import launch_ros.actions
+from launch_ros.actions import Node
 
 import rclpy
 from controller_manager.test_utils import (
@@ -49,6 +50,7 @@
     generate_load_controller_launch_description,
 )
 
+
 # Executes the given launch file and checks if all nodes can be started
 @pytest.mark.launch_test
 def generate_test_description():
@@ -133,7 +135,7 @@ def _assert_launch_result(self, result, min_len=0):
         return actions
 
     # ------------------------------------------------------------------
-    # Launch utility tests 
+    # Launch utility tests
     # ------------------------------------------------------------------
     def test_generate_controllers_spawner_from_list(self):
         controllers = ["test_controller_1", "test_controller_2"]