If you want to run the test cases in this project (you don't need to run them unless you want to contribute to this project), make sure you have the following environment variables defined:
export RINGCENTRAL_SERVER_URL=https://platform.ringcentral.com
export RINGCENTRAL_CLIENT_ID=
export RINGCENTRAL_CLIENT_SECRET=
export RINGCENTRAL_JWT_TOKEN=
export RINGCENTRAL_SENDER=
export RINGCENTRAL_RECEIVER=