wanderbooks/docs/testing.md

Testing strategy

How wanderbooks knows its books are right. Strongest oracle first: a test's worth is where its idea of "correct" comes from, not what it runs. Formal proofs are in docs/verification.md; the authorities every rule comes from are in docs/spec/. Scope so far: ledger-core in full, and the store's journal safety; the other crates come next (gap list).

Layers

Layer	Oracle (rank)	Where	Command	Runtime	Gates
Spec-derived examples	written specs with sources (1)	tests/spec_*.rs, invariants.rs, statements.rs, assets.rs, ...	just check	seconds	every change
Regressions	the bug, named (1)	beside the code they cover, *_regression/named for the defect	just check	seconds	every change
Compatibility contracts	journals written under older rules must open (1)	ledger-store/tests/store.rs (books_written_under_older_rules_still_open)	just check	<1s	every change
Properties	laws over all inputs (2)	properties.rs, spec_*.rs, kernel_bridge.rs	just check	seconds	every change
Metamorphic	scaling, reversal, ordering invariance (2)	spec_reports.rs	just check	seconds	every change
Refusal law (store)	a refused command never reaches the journal; the books reopen to the same reports (2, 3)	store.rs refused_commands_never_reach_the_journal	just check (STORE_CASES=5000 deeper)	~20s	every change
Fault injection (store)	a full disk or a cut-off append leaves whole, openable books (1)	ledger-store/tests/faults.rs, store.rs (power_loss_at_any_byte_of_the_last_append_is_recovered)	just check	~5s	every change
Concurrency (store)	a viewer reading while the books are written sees only whole books, never a false "differs" (2)	ledger-store/tests/concurrency.rs	just check	<1s	every change
Model-based stateful	the Lean state machine, transcribed (3)	tests/model.rs	just check	~3s	every change
Differential: Decimal vs i64	the kernel at two types (3)	kernel_bridge.rs	just check	<1s	every change
Differential: GnuCash	another implementation, adjudicated (3)	tests/oracle_gnucash.rs, oracle/gnucash/	just oracle	~2 min	weekly
Formal proofs	Kani (bounded) and Lean (unbounded)	src/proofs.rs, verify/lean/	just prove	~3 min	weekly
Fuzzing	crash, hang, broken books (4)	fuzz/fuzz_targets/, corpora in fuzz/corpus/	just fuzz <target> <secs>	10 min each	weekly
Miri	undefined behavior in our use of dependencies (4)	the core's unit, bridge, invariant tests	just miri	~2 min	on demand
Golden	tests/golden/fixture_company.json (5)	invariants.rs	just check	<1s	every change
Benchmarks	a baseline (6)	benches/books.rs	just bench	~1 min	none (no budget, by decision)
Mutation	can the tests fail?	ledger-core (2026-10-13: 1,011 caught + 13 timeouts of 1,024 viable, 0 missed)	just mutants	~3 h	weekly

CI: .github/workflows/check.yml runs just check on every push; scheduled.yml runs proofs, the oracle, fuzzing, and mutation weekly.

Seeds and failure databases: proptest's *.proptest-regressions files are checked in and replay on every run. The GnuCash oracle's books come from fixed seeds (SEED in oracle_gnucash.rs). Fuzz corpora live in fuzz/corpus/<target>.

Golden review: fixture_company.json is hand-verified (docs/oracle.md, Layer 1). The van depreciation golden was replaced on 2026-10-13 by a hand computation (van_schedule_is_the_hand_computed_one) after every row was checked against it.

Benchmarks (baseline 2026-10-13)

No budget, by decision (Stephen, 2026-10-13: the books do little work and are fast enough). The numbers are a baseline to spot a regression.

40-account chart, two-line entries across a year, on the development laptop:

	1k entries	10k entries
clone the ledger (store rehearsal, per command)	56 µs	1.0 ms
post one more entry	1.0 µs	5.8 µs
trial balance	44 µs	1.07 ms
balance sheet	47 µs	1.04 ms
one month's P&L	25 µs	248 µs

Formerly assumed: checked against the standards (2026-10-13)

Stephen isn't an accountant and won't adjudicate these; each was checked against published sources instead (rank: FASB ASC via the Deloitte DART reproduction, SEC, IRS; then textbooks; software practice is evidence of convention only). Verdicts: CONFIRMED (a source supports it), CONVENTION (no standard governs; matches mainstream practice), DESIGN (not an accounting question), CHANGE (a source says otherwise; work pending).

#	Behavior	Verdict	Source / note
1	A P&L whose start is after its end is refused	DESIGN	No standard governs a reversed range; refusing beats silently swapping a typo
2	A balance sheet omits zero-balance accounts	CONFIRMED	Reg. S-X 210.4-03(a): "No caption should be shown ... as to which the items and conditions are not present." A comparative statement must still show a zero beside a non-zero prior column
3	The lifetime profit_and_loss counts closing entries	CONFIRMED	Used as earnings not yet closed on the balance sheet; closed income is already in capital (OpenStax Principles of Financial Accounting 5.1). Its name misleads: rename to unclosed earnings (pending)
4	Closing a period with nothing to close still locks it	CONVENTION	A close is a lock (B-12); a dormant month must still lock and count for close-in-order
5	Draws and distributions are closed into capital at period end	CONFIRMED	OpenStax 5.1: dividends "are closed to the permanent account"; drawing accounts close to owner's capital. Monthly closes mean the year's K-1 Item L withdrawals sum across months
6	Reconciliation balances	CONFIRMED	Signed by the account's normal side (a card reads as owed), as statements show it; reconciling_a_card_reads_its_normal_side_...
7	A member's ending on one equity statement may differ by a cent from the next statement's beginning	CHANGED 2026-10-13	A capital account is one running balance (Form 1065 K-1 instructions, Item L). Undistributed earnings now split cumulatively as of each date, so each member's capital chains exactly (each_members_capital_chains_across_statements; it fails on the old code); rules.md B-13
8	Cash flow nets one line per account; investing comes only from registered assets	CHANGED 2026-10-13	ASC 230-10-45-7: gross receipts and payments "more relevant" than net; 45-8 limits netting to quick-turnover items. Financing and investing are now gross; loans made and investments bought are investing (230-10-20, 45-13) via [books] investing_accounts. Owner-advanced expenses: PwC 6.9.3.1 constructive treatment via [books] financing_accounts (rules.md B-14)
9	An asset's life ends at purchase + life months, that day not held; day-count proration	CONVENTION	Exactly N months of service; day proration and the mid-month convention are both accepted book policies (ASC 360-10-35-4 not read: login)
10	A payroll entry has one line per account total	CONFIRMED	The per-employee detail the IRS requires ("Amounts and dates of all wage ... payments", Employment Tax Recordkeeping) is kept in the run; a summary entry is standard
11	A period with exactly the dates of an existing one is allowed	DESIGN	Nothing governs duplicate periods; harmless (the second close locks only). Refusing exact duplicates is an option
12	Each close into members' capital rounds on its own (ties to the earlier member)	CHANGE (pending)	Found 2026-10-13 with #7: twelve monthly 50/50 closes can leave one member several cents ahead of half the year's income. Closes should split cumulatively too (year-to-date allocation minus what earlier closes gave); a new journaled rounding rule, older closes replaying as booked

Questions are settled from the sources, not by any one company's CPA (wanderbooks is general software). Where the standards leave a real choice, it is a per-company setting with a sourced default, for that company's accountant to review: the cash flow account roles (rules.md B-14) are the first.

Gap list: what isn't covered, and what would bring it in

Technique	Status	Trigger
Fault injection	SKIP for the core (no I/O, clock, or network); DONE for the store's journal (full disk, cut-off append)	the first I/O or clock in ledger-core
Integration	SKIP for the core (no collaborators)	the core gains one; covered at the store and MCP layers
End-to-end	SKIP for the core (a library)	MCP stdio tests cover the journeys
Security properties	SKIP for the core (no roles, no secrets)	the first permission concept, or a secret-bearing field
Concurrency stress	SKIP for the core (no shared state); DONE for the store's writer + viewer (found the false "differs")	the first Arc, atomic, or lock in the core; the MCP server's HTTP transport shares one store across sessions (next)
Lean: apportion's sum law for any n	OPEN	Kani covers n <= 3, properties n <= 5; needs a permutation lemma
ASC paragraphs not yet read	OPEN	ASC 360-10-35-4, 340-10, 230-10-45-10, 606-10-55-37B, 210: needs a FASB basic-view login
GnuCash's own close	OPEN	the oracle books closes as ordinary entries; comparing GnuCash's Close Book needs its Scheme API
Store: differential replay vs. projection, concurrency (writer + snapshot reader), benchmarks at 10k, mutation	NEXT	then import, MCP, config, GUI, the same playbook