While it is true that most tests are different from production, having a solid test suite can go a long way in moving with startup speed but breaking stuff as little as possible. We (as in me and a couple of others from our startup) have written a howto on using Docker and Ansible to build your test suite a few months ago. Strangely enough, it has almost the same title:
http://blog.mist.io/post/82383668190/move-fast-and-dont-brea...