There are some plugins that might require deploy artefacts into Mesos/Marathon and check some parameters to be sure that it has been deployed correctly.

It can be implemented in similar way as Docker support. It might look like:

@Marathon(app="org/jenkinsci/plugins/marathon/apps.json")
public class MarathonTest {
} 

Basically like DockerFixture, this annotation would read the Marathon json file used for starting a new application.

app attribute could be an optional attribute, and json file could be placed in a default location like Dockerfile location in DockerFixture.