testing

Run the harden script with a commit range such as `harden --range main..HEAD` in a clean repository. It mutates the functions your range touched using mutmut, compares survivors against the merge-base, and reports new survivors, uncovered lines, and unmeasured changes.

A test oracle is a source of expected values independent of the implementation, such as a spec sentence, worked example, or invariant property. Expectations recomputed the same way the code computes them agree with the code by construction, even when both are wrong.

No. mutmut mutates only top-level functions and methods of top-level classes, so changes to decorated functions, properties, and module-level statements are reported as unmeasured rather than silently treated as clean.

Harden mutates the tree it measures and reports results per commit, so uncommitted changes would be mutated without appearing in the measured range. A dirty tree is refused before any measurement begins.

Exit 0 means everything measured came back clean, exit 1 means findings such as a new surviving mutant or an uncovered changed line, and exit 2 means no findings but something could not be measured, such as unresolved mutants or unanalysable files.

Use property tests when a spec states something that must always or never hold, since the property becomes a check over generated inputs at its seam. Generate whole valid domain values rather than raw randomness so the generator explores the space the code actually meets.