So many +1s

> Developers of large or legacy systems that cannot already be run in their entirety during development often believe that it is impractical to run the entire system during development.

This is just a flat out ridiculous statement this author makes. My wife works on an automation system intended to respond to incoming events in the form of positive tips in surveillance system collections that in turn cues further tipping rules to retask those collection systems. One of the external dependencies is the entire spy satellite control system of the United States. How are you supposed to run this in your development environment? Some things you have to mock.