tests in google_sign_in uses the real method channel, which could cause failure after publishing changes in google_sign_in_platform_interface. These failures are not easy to catch as they don't fail when landing the change, but they fail until the change is published to pub.

See https://github.com/flutter/plugins/blob/master/packages/url_launcher/url_launcher/test/mock_url_launcher_platform.dart for an example of mock platform interface

We had a temp fix in flutter/plugins#3690 for one of such failures.