In the recently merged #236, @pierreglaser added the ability to launch the tests of some downstream projects (loky, joblib and dask/distributed) in order to be able to detect if a specific PR is likely to introduce a regression in a downstream project just by adding the [ci downstream] flag in a commit message of the last commit of the PR.

It would be great to add the build configuration to launch the Ray test suite in a similar manner.

I also opened #237 to do the same for PySpark.