This tool generates deterministic JavaScript probes, runs each probe under Node and Ant, and compares the complete process result: exit status, signal, timeout state, stdout, and stderr. Probe output uses a canonical JSON encoding for values that JSON normally loses, including undefined, non-finite numbers, BigInts, errors, functions, and cycles.

The families cover property semantics, RegExp behavior, Promise and microtask timing, readable/writable stream property shape, and path resolution. Stream probes are atomic: each generated case checks one property or one target's own keys, so a broad mismatch does not contaminate unrelated generated cases. Path probes cover POSIX cwd resolution plus Win32 drive-relative, rooted, drive, and UNC behavior.

Run one deterministic pass across every family:

node tests/differential/runner.mjs

Generate more cases for selected families and minimize mismatches:

node tests/differential/runner.mjs \
  --family property \
  --family regexp \
  --seed 42 \
  --cases 20 \
  --minimize

Minimized standalone .cjs repros are written to differential-output/ by default. Use --output to choose another location and --json for newline-delimited machine-readable output.

The runner exits 0 when all probes match, 1 when it finds a mismatch, and 2 for invalid configuration or a missing executable. A mismatch is a finding, not necessarily an Ant bug: Node version differences and intentionally unsupported surfaces still require classification.

Run its Node-side unit checks with node tests/differential/test.mjs.