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Mutation Testing (#378)

Overview

Mutation testing verifies that the test suite actually catches logic errors. A mutant is a copy of the source with one small change (e.g. > → >=, true → false). If all tests still pass for a mutant, the test suite has a gap.

Tool

cargo-mutants — install with:

cargo install cargo-mutants

Running

# Both contracts
cargo mutants -p ip_registry -p atomic_swap

# Single contract
cargo mutants -p ip_registry

Configuration is in .cargo-mutants.toml at the repo root.

Mutation-Catching Tests

Dedicated tests live in src/mutation_tests.rs for each contract. They are designed to kill the most common mutant classes:

Mutant class Killed by
Remove zero-hash check zero_hash_is_rejected
Off-by-one in ID counter ids_are_sequential_starting_at_one
Remove duplicate-hash check duplicate_hash_is_rejected
Flip revoked = true revoked_flag_is_set_after_revoke
Skip owner-index append owner_index_contains_committed_ids
Always-true verify verify_commitment_rejects_wrong_secret
Always-false verify verify_commitment_accepts_correct_secret
Skip status → Pending initiate_swap_sets_pending_status
Skip status → Accepted accept_swap_sets_accepted_status
Skip status → Completed reveal_key_sets_completed_status
Skip commitment verification reveal_key_rejects_wrong_secret
Remove price > 0 check zero_price_is_rejected
Allow double-accept accept_swap_twice_is_rejected
Allow reveal on Pending reveal_key_on_pending_swap_is_rejected

Interpreting Results

  • Killed — the mutant caused at least one test to fail. Good.
  • Survived — no test caught the mutation. Add a test targeting that line.
  • Timeout — the mutant caused an infinite loop. Treated as killed.
  • Unviable — the mutant did not compile. Ignored.

Baseline Results

Mutation testing was run against the current codebase. All mutants in the core validation paths (require_non_zero_commitment, require_unique_commitment, require_positive_price, status transition assignments) are killed by the mutation_tests module.

CI/CD Integration (#556)

Mutation testing runs automatically via .github/workflows/mutation.yml:

Trigger Scope
Pull request Only lines changed in the PR diff (--in-diff) — fast
Weekly schedule (Mon) Full sweep over both contracts
Manual dispatch Full sweep

The PR-scoped run keeps feedback fast while ensuring new/changed logic is covered by mutation-killing tests. The full report is uploaded as the mutants-report build artifact (mutants.out/).

If a PR introduces a surviving mutant, add a test (typically in src/mutation_tests.rs) that fails for that mutation, then re-run.