launch_test does not return and shows ValueError: generator already executing

I am trying to run a test using launch_test but it shows "ValueError: generator already executing". In this case, the launch_test does not return. Therefore, I have to terminate the process by pressing Ctrl + C. Below is the complete info reported at terminal:

$ launch_test src/minimal_service/test/test_service_member_function.py 
[INFO] [launch]: All log files can be found below /home/ravi/.ros/log/2022-08-01-19-42-08-016668-dell-96224
[INFO] [launch]: Default logging verbosity is set to INFO
[INFO] [service_member_function-1]: process started with pid [96228]
test_srv_1 (test_service_member_function.TestMinimalServiceNode) ... ok
test_srv_1_exists (test_service_member_function.TestMinimalServiceNode) ... [WARN] [1659350528.358283962] [rcl.logging_rosout]: Publisher already registered for provided node name. If this is due to multiple nodes with the same name then all logs for that logger name will go out over the existing publisher. As soon as any node with that name is destructed it will unregister the publisher, preventing any further logs for that name from being published on the rosout topic.
Exception in thread Thread-2:
Traceback (most recent call last):
  File "/usr/lib/python3.8/threading.py", line 932, in _bootstrap_inner
    self.run()
  File "/usr/lib/python3.8/threading.py", line 870, in run
ok
test_srv_2 (test_service_member_function.TestMinimalServiceNode) ...     self._target(*self._args, **self._kwargs)
  File "/opt/ros/galactic/lib/python3.8/site-packages/rclpy/__init__.py", line 196, in spin
Exception in thread Thread-3:
Traceback (most recent call last):
  File "/usr/lib/python3.8/threading.py", line 932, in _bootstrap_inner
    executor.spin_once()
  File "/opt/ros/galactic/lib/python3.8/site-packages/rclpy/executors.py", line 704, in spin_once
    self.run()
  File "/usr/lib/python3.8/threading.py", line 870, in run
    handler, entity, node = self.wait_for_ready_callbacks(timeout_sec=timeout_sec)
  File "/opt/ros/galactic/lib/python3.8/site-packages/rclpy/executors.py", line 690, in wait_for_ready_callbacks
    self._target(*self._args, **self._kwargs)
  File "/opt/ros/galactic/lib/python3.8/site-packages/rclpy/__init__.py", line 196, in spin
    return next(self._cb_iter)
ValueError: generator already executing
    executor.spin_once()
  File "/opt/ros/galactic/lib/python3.8/site-packages/rclpy/executors.py", line 704, in spin_once
    handler, entity, node = self.wait_for_ready_callbacks(timeout_sec=timeout_sec)
  File "/opt/ros/galactic/lib/python3.8/site-packages/rclpy/executors.py", line 690, in wait_for_ready_callbacks
    return next(self._cb_iter)
ValueError: generator already executing
^C[WARNING] [launch]: user interrupted with ctrl-c (SIGINT)
[service_member_function-1] Traceback (most recent call last):
[service_member_function-1]   File "/home/ravi/ros2_ws/install/examples_rclpy_minimal_service/lib/examples_rclpy_minimal_service/service_member_function", line 33, in <module>
[service_member_function-1]     sys.exit(load_entry_point('examples-rclpy-minimal-service==0.9.4', 'console_scripts', 'service_member_function')())
[service_member_function-1]   File "/home/ravi/ros2_ws/install/examples_rclpy_minimal_service/lib/python3.8/site-packages/examples_rclpy_minimal_service/service_member_function.py", line 31, in main
[service_member_function-1]     rclpy.spin(node)
[service_member_function-1]   File "/opt/ros/galactic/lib/python3.8/site-packages/rclpy/__init__.py", line 196, in spin
[service_member_function-1]     executor.spin_once()
[service_member_function-1]   File "/opt/ros/galactic/lib/python3.8/site-packages/rclpy/executors.py", line 704, in spin_once
[service_member_function-1]     handler, entity, node = self.wait_for_ready_callbacks(timeout_sec=timeout_sec)
[service_member_function-1]   File "/opt/ros/galactic/lib/python3.8/site-packages/rclpy/executors.py", line 690, in wait_for_ready_callbacks
[service_member_function-1]     return next(self._cb_iter)
[service_member_function-1]   File "/opt/ros/galactic/lib/python3.8/site-packages/rclpy/executors.py", line 588, in _wait_for_ready_callbacks
[service_member_function-1]     wait_set.wait(timeout_nsec)
[service_member_function-1] KeyboardInterrupt
[ERROR] [service_member_function-1]: process has died [pid 96228, exit code -2, cmd '/home/ravi/ros2_ws/install/examples_rclpy_minimal_service/lib/examples_rclpy_minimal_service/service_member_function --ros-args -r __ns:=/'].
Processes under test stopped before tests completed
Process 'service_member_function-1' exited with -2
##### 'service_member_function-1' output #####
Traceback (most recent call last):
  File "/home/ravi/ros2_ws/install/examples_rclpy_minimal_service/lib/examples_rclpy_minimal_service/service_member_function", line 33, in <module>
    sys.exit(load_entry_point('examples-rclpy-minimal-service==0.9.4', 'console_scripts', 'service_member_function')())
  File "/home/ravi/ros2_ws/install/examples_rclpy_minimal_service/lib/python3.8/site-packages/examples_rclpy_minimal_service/service_member_function.py", line 31, in main
    rclpy.spin(node)
  File "/opt/ros/galactic/lib/python3.8/site-packages/rclpy/__init__.py", line 196, in spin
    executor.spin_once()
  File "/opt/ros/galactic/lib/python3.8/site-packages/rclpy/executors.py", line 704, in spin_once
    handler, entity, node = self.wait_for_ready_callbacks(timeout_sec=timeout_sec)
  File "/opt/ros/galactic/lib/python3.8/site-packages/rclpy/executors.py", line 690, in wait_for_ready_callbacks
    return next(self._cb_iter)
  File "/opt/ros/galactic/lib/python3.8/site-packages/rclpy/executors.py", line 588, in _wait_for_ready_callbacks
    wait_set.wait(timeout_nsec)
KeyboardInterrupt
##############################################

Required Info:

• Operating System:
  • Ubuntu 20.04.4 LTS
• Installation type:
  • binaries
• DDS implementation:
  • default
• Client library (if applicable):
  • rclpy

Question

How to test all the services in my node?

Code

• test_service_member_function.py

  from threading import Thread
  import unittest
  
  import launch
  import launch_ros
  import launch_testing
  import pytest
  import rclpy
  from std_srvs.srv import SetBool, Trigger
  from example_interfaces.srv import AddTwoInts as AddTwoI
  
  
  @pytest.mark.rostest
  def generate_test_description():
      node = launch_ros.actions.Node(
          package='examples_rclpy_minimal_service',
          namespace='',
          executable='service_member_function',
      )
      return (
          launch.LaunchDescription(
              [
                  node,
                  # Start tests right away - no need to wait for anything
                  launch_testing.actions.ReadyToTest(),
              ]
          ),
          {
              'minimal_service_node': node,
          },
      )
  
  
  class TestMinimalServiceNode(unittest.TestCase):
  
      @classmethod
      def setUpClass(cls):
          # Initialize the ROS context for the test node
          rclpy.init()
  
      @classmethod
      def tearDownClass(cls):
          # Shutdown the ROS context
          rclpy.shutdown()
  
      def setUp(self):
          # Create a ROS node for tests
          self.node = rclpy.create_node('test_minimal_service_node')
  
          # Creating service clients
          self.client_1 = self.node.create_client(AddTwoI, 'srv_1')
          self.client_2 = self.node.create_client(SetBool, 'srv_2')
          self.client_3 = self.node.create_client(Trigger, 'srv_3')
  
          self.assertTrue(self.client_1.wait_for_service(timeout_sec=5.0))
  
          # Create a spin thread for synchronous service call
          self.spin_thread = Thread(target=rclpy.spin, args=(self.node,))
          self.spin_thread.start()
  
      def tearDown(self):
          self.node.destroy_node()
  
      def test_srv_1_exists(self):
          self.assertTrue(self.client_1.wait_for_service(timeout_sec=5.0))
  
      def test_srv_2_exists(self):
          self.assertTrue(self.client_2.wait_for_service(timeout_sec=5.0))
  
      def test_srv_3_exists(self):
          self.assertTrue(self.client_3.wait_for_service(timeout_sec=5.0))
  
      def test_srv_1(self):
          req = AddTwoI.Request(a=10, b=20)
          res = self.client_1.call(req)
          self.assertEqual(res.sum, 30)
  
      def test_srv_2(self):
          req = SetBool.Request(data=True)
          res = self.client_2.call(req)
          self.assertEqual(res.message, 'Hello from SetBool Service')
  
      def test_srv_3(self):
          req = Trigger.Request()
          res = self.client_3.call(req)
          self.assertEqual(res.message, 'Hello from Trigger Service')
  ```
  

• service_member_function.py

  import rclpy
  from rclpy.node import Node
  from std_srvs.srv import SetBool, Trigger
  from example_interfaces.srv import AddTwoInts as AddTwoI
  
  
  class MinimalService(Node):
  
      def __init__(self):
          super().__init__('minimal_service')
          self.srv_1 = self.create_service(AddTwoI, 'srv_1', self.srv_1_cb)
          self.srv_2 = self.create_service(SetBool, 'srv_2', self.srv_2_cb)
          self.srv_3 = self.create_service(Trigger, 'srv_3', self.srv_3_cb)
  
      def srv_1_cb(self, req, res):
          res.sum = req.a + req.b
          return res
  
      def srv_2_cb(self, req, res):
          res.message = 'Hello from SetBool Service'
          return res
  
      def srv_3_cb(self, req, res):
          res.message = 'Hello from Trigger Service'
          return res
  
  
  def main(args=None):
      rclpy.init(args=args)
      node = MinimalService()
      rclpy.spin(node)
      rclpy.shutdown()
  
  
  if __name__ == '__main__':
      main()
  

Additional Info

Please note that all the services returns peacefully when called from terminal using ros2 service call .... Anyway, below is the workspace structure:

.
├── build
├── install
├── log
└── src
    └── minimal_service
        ├── CHANGELOG.rst
        ├── examples_rclpy_minimal_service
        │   ├── __init__.py
        │   ├── service_member_function.py
        │   └── service.py
        ├── package.xml
        ├── README.md
        ├── resource
        │   └── examples_rclpy_minimal_service
        ├── setup.cfg
        ├── setup.py
        └── test
            ├── test_copyright.py
            ├── test_flake8.py
            ├── test_pep257.py
            └── test_service_member_function.py

The package minimal_service has been taken from ros2/examples.

Start with test/test_service_member_function.py and the launch_test invocation, then inspect the rclpy.spin calls and the service-client setup shown in the report. Reproduce the generator error with the listed service tests and determine the expected way to run all services without hanging; done means the test command completes without the ValueError.