FA-58108 / Double-entry ledger accounting / Member archive

FIFO perpetual inventory journal: return quantity check · case 03

Returning an entire purchase layer is rejected.

Member previewVariant 3 · 3 implementations · 7 checks per implementation

Case contract

x = [['buy', qty, unit_cost] | ['sell', qty, unit_price] | ['purchase_return', qty, unit_cost]]. Layers are kept oldest first; a buy at the same cost as the newest layer merges into it. A sale consumes layers oldest first (COGS) and records revenue; a sale exceeding on-hand quantity is rejected whole. A purchase return removes qty from the newest layer at that cost holding at least qty, else it is rejected. Emptied layers are removed. Return {'cogs', 'revenue', 'inventory': sum qty*cost, 'layers', 'rejected': event indexes}.

Why this case matters

Ledger software must keep debits equal to credits and apply normal-balance, period and cutoff rules exactly; small sign or boundary slips silently misstate financial statements.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression: return quantity check	`{"cogs": 0, "inventory": 1700, "layers": [[10, 120], [2, 150], [2, 100]], "rejected": [0, 1, 2, 3, 4, 8], "revenue": 0}`	`{"cogs": 0, "inventory": 1400, "layers": [[10, 120], [2, 100]], "rejected": [0, 1, 2, 3, 4], "revenue": 0}`	Failed

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