Ask HN: What techniques do you use to speed up your tests suite?

In our build, functional/integration specs/tests tend to take up the bulk of the time. This can be a real pain when trying to ship code more quickly, and the wait-pain is very real between pushing something to a build and waiting for the code to be "green."

I'm interested in techniques that speed things up. We work in Ruby and JS, for reference, but any tips appreciated.