Making Cloud Code Testable

Developers seem to assume that just because their application code may now interact with the cloud (e.g. read/write data from AWS S3 buckets, invoke AWS lambda functions, email via AWSD SES, send or receive AWS SMS messages, etc.) that it's no longer reasonable or easy to structure their code in a testable way without access to the cloud. Yes, my examples are AWS centric. The principles in this blog post apply to Azure or Google Cloud code as well.
By "testable" I mean unit tests that don't re...