Mutation testing finds behavior no check constrains. For solidcore the useful
question is two-tier: a mutant matters only if neither the package's unit tests
nor the unit's difftest notices.
scripts/mutants.sh runs cargo-mutants (unit tests) on a module, a shard or a PR
diff, then patches each unit-test survivor into the working tree and replays it
against difftest --unit <id>, classifying it as caught-by-difftest or
both-tier-missed. Docker mode reuses one container for the replays; the script
prefers the pinned rustup toolchain and runs under nice with CARGO_BUILD_JOBS=2.
docs/mutation-testing.md documents the method, measured costs (~16 s/mutant,
~1 min/survivor), triage, and a CI proposal (per-PR in-diff tier 1, nightly
sharded tier 2), with the pilot findings: topology.topology's change-tracker
bookkeeping is unconstrained by both tiers.
reports/mutants/ is gitignored.
Co-Authored-By: Claude Code <noreply@anthropic.com>
Thijs Damsma