Cargo-mutants:zombie: Inject bugs and see if your tests catch them

This is a cool project. Related fun anecdote: I once found an application at work where just about the ENTIRE test suite was a no-op as the author (and subsequent copy-pasters) misunderstood a GTest feature. Yep, dozens of unit tests which did not actually test anything. Fortunately the application did mostly work and wasn't critical. Experiences like these make me want to write "negative tests" to test test failure conditions.

That's why I practice "red, green, refactor". I must see a new test fail once before I believe that its passing means anything

This generalizes into the strategy that learning and programming are both skimming the edge of an envelope, alternating between things that work and things that almost work