This is cool. I like the idea quite a bit. This definitely solves a problem that I've thought about quite a bit, and have taken a stab at with one-off scripts.

This is cool. I like the idea quite a bit. This definitely solves a problem that I've thought about quite a bit, and have taken a stab at with one-off scripts. What I don't quite like is the fact that as one's expectations become more complex, one has to start encoding that logic into YAML with this custom assertion/pattern matching DSL as shown in the README. I think this might be more easily adopted if it could be integrated into an existing testing framework, allowing to developers to use our familiar patterns of assertions, and use the tools that we're already familiar with.