Two related cleanups in one commit, both surfaced by reading fox's
test_t3_bound_calculator.py (51 tests for my T3 calculator):
1. Refresh stale §7 numbers in the T3 bound doc
=================================================
fox's test_baseline_matches_section_11_doc docstring (lines
56-61) flagged that my §7.1 worked example said
622.7 / 290.0 / 32.7 bits but the calculator's actual
closed-form output is 625.87 / 292.48 / 33.39. Same drift in
§7.2 (3358 → 3387.72) and §7.3 (247 → 247.14).
The numbers were rounded estimates from when I drafted the doc
before the calculator existed. Refreshed all three §7 numeric
examples to match the calculator's actual output (verified live
via t3_bound_bits()). §3 inline approximation likewise updated
(290 → 292.48). Added a short note pointing readers at the
calculator + tests as the source of truth.
2. Backfill anchor_prg tests with fox's patterns
=================================================
fox's test_t3_bound_calculator.py demonstrated four patterns I'd
missed in my #000035 phi_prg tests:
- **Output prefix invariant** (closure check): phi_prg(h, n+k)[:n]
≡ phi_prg(h, n). Streaming-counter invariant — would catch a
bug where a per-call seed mutation broke determinism across
dim_h values.
- **Output length monotonicity**: len(phi_prg(h, n)) == n exactly.
Parametrized over n ∈ {1, 2, 4, 7, 16, 17, 64, 1024}. Catches
off-by-one in `_expand` truncation.
- **Hand-computed first block**: assert that the first 64 bytes
of output equal a direct ``hmac.new(seed, h + b'\\x00\\x00
\\x00\\x00', sha512).digest()``. Pattern from fox's
test_b1_exact_formula — don't rely on KAT regression alone;
compute the first-principles math in the test file. Catches
algorithm drift the KAT (regenerated against a buggy version)
would miss.
- **Seed-bleed check**: changing the seed must change EVERY output
position. Probability of false-positive ≈ 64 · 2^-32 ≈ 2^-26;
none expected in practice.
- **Parametrized invalid-input tests**: collapsed N separate
``test_rejects_*`` functions into ``@pytest.mark.parametrize``
cones (4 wrong-size-hash cases + 3 non-positive-dim_h cases).
Same coverage, fewer test functions.
Test count: was 20 in test_anchor_prg.py; now 27 (+7 from
parametrize expansion + new patterns). Full suite: 1720 → 1727.
Hygiene
=======
- make test → 1727 passed, 45 skipped.
- make chain-check-shards → 0 across all 7 shards.
- All new tests use ``pytest.importorskip`` already at module top
(anchor_prg has no extras gate; tests run unconditionally).
Lessons captured
================
The patterns to remember for future calculator/probe-style code:
1. KAT regression alone isn't enough. Add hand-computed
formula tests so the math itself is asserted in the test
file, not just "consistent with a recorded snapshot".
2. Test monotonicity / closure invariants. They catch
algorithm drift, sign errors, missing terms.
3. Parametrize invalid-input tests. One function, N cases.
4. Test the doc's numbers against the function. Catches
calibration drift in the doc itself (this commit's
finding about §7).
5. CLI subprocess tests for end-to-end. Argparse + main()
drift the import-only tests miss.
russell@unturf.com
de997f7be3