To perform a full integration test, you need a valid "firebase-service-account.json" file.
The tests will create a Firebase user with the ID "Io2cPph06rUWM3ABcIHguR3CIw6v1" and write and read a document to/from "tests/test". Ensure read/write access via firebase rules.
A refresh and access token is generated. The refresh token is stored in "refresh-token-for-tests.txt" and will be reused for further tests. The reason being that Google allows only about 50 simultaneous refresh tokens at any time, so we do not want to create a new one each test run.