Latest Swarm suggests use of the update parameter in the review/build to show running and some (hopefully) meaningful message(s).

The "update" (instead of pass and fail) also as formatted in JSON in the body of the POST request. Test status: valid test status values are running, pass, and fail. Messages: you can pass a maximum 10 messages, if you provide more than 10 messages only the first 10 are saved. 

See https://www.perforce.com/manuals/swarm/Content/Swarm/admin.integrate_test_suite.html?Highlight=update