Hi,

I created a bunch of "unit-tests" for the static executor.
They test the following scenarios:

1. add 1 pub node and 1 sub node to the executor and spin
2. add 1 pub node to the executor and spin, then add 1 sub node while spinning
3. add 1 pub node and 1 node with no entities to the executor and spin, then add 1 sub to the second node while spinning
4. add 1 pub node and 1 sub node to the executor and spin, then while spinning remove the sub node from the executor

You can find them here
https://github.com/alsora/ros2-code-examples/blob/master/simple_static_executor/static_executor_test.cpp

These tests are meant to be used with your rclcpp version (nobleo/feature/static_executor), I opened the ticket here since it was not possible in that repo.

To build colcon build --packages-select simple_static_executor
To run ./install/simple_static_executor/lib/simple_static_executor/static_executor_test 2
Where the number at the end denotes the id of the test you want to run (1, 2, 3, 4)

The results are unfortunately not good.

Test 2 throws an exception

[ERROR] [1584978899.809709877] [rclcpp]: Couldn't add guard_condition to wait set: guard_conditions set is full, at /root/ros2_ws/src/ros2/rcl/rcl/src/rcl/wait.c:456
terminate called after throwing an instance of 'std::runtime_error'
  what():  Couldn't fill wait set
Aborted (core dumped)

In test 4 the subscription keeps receiving messages after having been removed from the executor

Could you have a look at the test?
Maybe I'm not using the executor as it is supposed to be used.

FYI the standard SingleThreadExecutor allows to pass all the tests successfully.

@MartinCornelis2 @mauropasse