Right now, if a method or service is marked as deprecated, gax.warn is used to emit a deprecation warning. However, this inadvertently causes builds to fail, as Mocha picks up on the deprecation warnings.

Therefore, it would be prudent to replace gax.warn with a sinon stub so marking a method/service as deprecated does not break the builds.

The interim fix is to disable the deprecation warning in unit tests by setting the CI variables.