All supported DevTest releases.
Have not used it but the documentation is here https://cloud.google.com/pubsub/docs/publisher
You could create a JavaScript step and execute it.
You will need Credentials from Google sample script we got from:
https://cloud.google.com/pubsub/docs/reference/rest/v1/projects.topics/publish?apix_params=%7B%22topic%22%3A%22projects%2Fdemos-esd-ct-presales%2Ftopics%2FCT-GC-Test-Pub-Sub%22%2C%22resource%22%3A%7B%22messages%22%3A%5B%7B%22attributes%22%3A%7B%22name%22%3A%22wrench%22%2C%22mass%22%3A%221.3kg%22%2C%22count%22%3A%223%22%7D%7D%5D%7D%7D
See attached file Google-Pu-SubJS.txt
It is really just a REST call, but the Oath means you have to get a Token first.
Rename to Google-Pu-SubJS.txt to Google-Pu-SubJS.js
But it is just a sample not a solution.
If this does not work, suggest you post this requirement on the Service Virtualization Communities forum:
https://community.broadcom.com/enterprisesoftware/communities/communityhomeblogs?CommunityKey=94bda077-625b-4914-8ac3-c88a06c2cc23