To run individual tests, run npm run local to start the firebase emulator. Otherwise, npm test will start the emulator then run the tests.
While tests are running, http://localhost:9000/.json?ns=testDb will show the state of the local database.
Other than npm dependencies, the local version of firebase installed with @firebase/testing also requires that java is installed locally.
To test in Cloud Build, the docker image needs both npm and java installed. docker/Dockerfile specifies how to create such an image, and you can use Cloud Build to publish the image by running
export CLOUDSDK_CORE_PROJECT=firesocket-test
gcloud builds submit --config cloudbuild.yaml .