kimera

https://github.com/giacope/kimera

Mutation testing for Ruby and Rails built on mutant schemata (Untch, Offutt & Harrold, 1993), as popularized by Stryker. All mutants for a file compile into one guarded-dispatch program selected at runtime, so there is no reparse or reload per mutant. A warm worker pool runs mutants in parallel, and diff-driven incremental runs gate CI.