David Heinemeier Hansson

The post discusses the idea of moving continuous integration back to developer machines and the advantages of running tests locally.

We're moving continuous integration back to developer machines

I think another item here is trust and scalability- 37signals is a sub-100 organization, and if you subtract the people who aren’t involved in development contributions (support, IT, QA, sales, marketing…etc) you have a rather small pool of developers/small team spread- so you can trust that the people who have contributing code to a project have familiarity.
This doesn’t scale as well to a larger organization where you can’t have as much oversight over developers and other teams- especially if you have large pools of shared code but different responsibility stacks- it’s trivial to just run <code>git commit --no-verify</code> or <code>git push --no-verify</code> and skip local CI- and in scenarios where contributor trust may be limited, remote CI is an excellent verification that crapcode isn’t being pushed.

I think it depends on what you are integrating. The problem with Shopify or GitHub is not the lines of code it’s the breadth of services you’d need to host on a single machine.
If you need to provision every service you’re going to hit a limit. Alternatively, if the code under test doesn’t include everything you could host a trunk build of those services in a lower environment. You’d also need to account for databases, caching servers, message buses, etc.
The idea of waiting to integration test your code on someone else’s computer is dumb though, and it doesn’t provide as much value (or timely feedback) as you’d think.