I'm trying to make use of the unit tests in testrmwimplementation, but it'll only ever use the default rmwcycloneddscpp implementation, and no others.

I've built with the command

colcon build --merge-install --cmake-force-configure --cmake-args '-DRMW_IMPLEMENTATION=rmw_fastrtps' --packages-select rmw_implementation test_rmw_implementation 

And ran with the commands

export RMW_IMPLEMENTATION=rmw_fastrtps_cpp
colcon test --merge-install --packages-select test_rmw_implementation

Yet when I examine the log for testrmwimplementation, it still uses cyclonedds instead of the specified fastrtps.

What am I doing wrong? Is there a guide for this?