[composition] Enable tests

[SuperJappie08]

Description

Enables the API launch tests of the composition package (in some workable form)

Fixes #747

Is this user-facing behavior change?

No

Did you use Generative AI?

No

Additional Information

I do not use a generated substitution anymore, since it was unclear which binary path would have matched:

• API_COMPOSITION_EXECUTABLE
• API_COMPOSITION_CLI_EXECUTABLE

[SuperJappie08]

I must add that the tests seem a bit flaky locally; maybe waiting for a process start event or delay before loading the components could help.

Another option is to migrate to launch_ros component actions (ComposableNodeContainer and LoadComposableNodes)

[fujitatomoya]

@SuperJappie08 thanks for trying to fix this.

obviously this is missing as you pointed out.

i am not sure about this fix. instead API_COMPOSITION_EXECUTABLE should be added to CMakeLists.txt just like the others such as MANUAL_COMPOSITION_EXECUTABLE?

[SuperJappie08]

@fujitatomoya, I tried that, but it was unclear to me which executables those fields should be. (because of the reason given below and the --delay argument)

I tried my current solution (using ros2component) in those fields.
However, ExecuteProcess wants space-separated arguments for the command.
So that would mean it would turn into [*'@API_COMPOSITION_EXECUTABLE@'.split(), ...], which did not feel correct.

I could change it to be like that if that would be better.

[SuperJappie08]

I've done some looking around, and the test was disabled in #319.
In that PR, the rclcpp_components was introduced, and the custom api_composition(_cli) was removed.

The substitutions probably were used since it was a local compile target of this package.

So I think the best way forward is most likely to use the launch_ros component API, since it prevents having to depend on ros2component.