It would be great that we could execute only one level 

On Plone test infraestructure we have the robot tests on different level from the normal tests and we would like to configure jenkins to execute only robot tests on a job.

Now we are using -t robot but its a bit hacky.
From the name I would assume that the intended behavior would be `bin/test --at-level=2 --only` if you wanted to run level 2 tests but not level 3 tests.  From the `type="int"` bit I'm guessing that you actually need to use `bin/test --only=2`.

Can you change the option name to `--only-level`?  getopt lets you truncate, so you'll still be able to type `bin/test --only`, but I think the similarity with `--at-level` will make it clearer.

Also, yes, this is unlikely to get merged without tests.