Mutation-tested vector's unit suite: zero survivors across 100 mutants

[fohara]

I ran a mutation-testing pass over vector's unit suite recently and wanted to share the result, since it is unusually good.

Setup: upstream master in a Docker fixture, mutants generated across 15 source files under src/, coverage-guided selection, each mutant run against the tests that cover it and validated with the full suite where targeting could not narrow it. 100 mutants executed.

Every one of them was caught. For anyone who works on the suite: that does not happen often!

One footnote on the 100: 18 of the mutants never made it past the compiler, so the tests themselves get credit for 82 of the catches. Rust's type system does a lot of the work here, which is worth remembering whenever mutation scores get compared across languages.

I discovered these results while mutation-testing this repo (I'm building a tool in this space). Happy to share the full run output or the fixture setup if anyone wants to reproduce it.