Today, I'll share a trademark secret that allows us to move fast and make huge changes without fear. When we're starting a new [Symfony 2.8-7.2 upgrade project](/blog/off-the-beaten-path-to-upgrade-symfony-28-to-72), we cover it with a couple of tests first. These tests are not units, but smoke tests - with a couple of lines they cover a huge portion of the Symfony framework layer we use. With a couple of lines, we can cover complex container operations and avoid most dummy yet destructive bu...
