Running server and client tests seperately

Hello, I would like to run server or client tests separately. I do not find this option neither in meteor nor in mocha docs. I run this command to start tests:

TEST_BROWSER_DRIVER=nightmare meteor test --once --driver-package meteortesting:mocha

Then first the server tests will be executed and the client tests afterward. Placing some describe.only in the code does not have the desired effect. That only effects the environment of the test, server or client.

Is there an option like --client-only for “meteor test”?