Add fast-check property tests for placeholder and pii-redact Luhn#136
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Property-based tests cover invariants that example-based tests can't easily enumerate: that `replaceMatchesInTextNode` preserves all non-matched text, emits exactly one inline placeholder per disjoint match, and round-trips through reveal back to the original text; and that the PII detector masks every Luhn-valid card number while leaving Luhn-invalid digit runs of the same shape alone. Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>
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Summary
fast-checkas a dev dependency inextension/.replaceMatchesInTextNode(extension/src/lib/__tests__/placeholder.property.test.ts): no-op on empty matches; one inline placeholder per disjoint match; non-matched text preserved exactly and in order; reveal round-trips back to the original text; overlapping matches are dropped, not double-replaced.pii-redact(extension/src/rules/__tests__/pii-redact.property.test.ts): every Luhn-valid 13–19-digit number is masked; the same numbers with a single-digit flip (Luhn-invalid, same shape) are left alone.Why fast-check here
These two surfaces have small invariants that are tedious to enumerate by example: the placeholder replacer is cursor-driven and easy to break on overlap/order changes, and the Luhn check sits behind a regex that admits many digit shapes the checksum then has to reject. Property tests give us a regression net for refactors without us having to hand-build cases at every boundary.
Test plan
bun run preflight— biome, eslint, tsc (src + tests), knip, jest with coverage (1015 tests, both new suites included).🤖 Generated with Claude Code