Running the Android emulator is not currently supported on CircleCI, since it's not supported by the type of virtualization CircleCI uses on Linux. We recommend using an external service such as Firebase Test Lab to run your emulator tests from your CircleCI job.
You can use the gcloud Command Line to do this. (We're working on documenting a full example to help get this set up. If you get something working, do let us know on Discuss.) The gcloud tools are preinstalled on the CircleCI Docker images for Android - see the Dockerfiles here and Docker Hub links here.