Firebase Test Lab on pipelines

Good day first time here, I am enjoying working with Bitbucket Pipeline as it is simple and easy to understand with good and clear documentation. However I need to deploy/upload the apk from a step artifact using gcloud command and I can’t see any related article or topic on this yet.

This is the Firebase Test Lab documentation using gcloud CLI.

So far I just received a message from Twitter that I should refer to this

But as far as I can tell this documentation is about deploying an app to Google App Engine which is not in my case.