def METHOD_NAME(self, source_app, app_storage):
    # Given a source in the DB
    passphrase = PassphraseGenerator.get_default().generate_passphrase()
    source_user = create_source_user(
        db_session=db.session,
        source_passphrase=passphrase,
        source_app_storage=app_storage,
    )
    # When they try to authenticate using their passphrase
    authenticated_user = authenticate_source_user(
        db_session=db.session, supplied_passphrase=passphrase
    )
    # It succeeds and the user is mapped to the right source in the DB
    assert authenticated_user
    assert authenticated_user.db_record_id == source_user.db_record_id