← BBS SG Bank submission · All documents
Derived from the observed behaviour of legacy/bank.cob. The modern implementation must match legacy semantics exactly, plus satisfy the modernization non-functionals. Every test below is re-runnable.
Result date: 2026-09-23 · Environment: python3 3.14, isolated GnuCOBOL 3.2.0 (/tmp/gcb-build/install/bin/cobc). Runners: scripts/test_bank.py (33 tests), tests/test_modern.py (5 tests), the site/tests/ suite (50 tests) and legacy-ui/tests/test_terminal.py (20 tests), plus the manual fixture below. These executable local suites total 108 passing tests; the Forge Testing v1 artifact (docs/forge/testing.md, 132 proposed cases) is a separate planning document, not an execution record.
| ID | Requirement | Source of truth |
|---|---|---|
| FR-1 | Process every record in operations.dat in file order, applying kinds D (deposit), W (withdraw), T (transfer). | bank.cob L65-171 |
| FR-2 | Reject an operation whose kind ∉ {D, W, T}. | bank.cob L99-103 |
| FR-3 | Reject an operation whose amount is non-positive or not a 12-digit numeric. | bank.cob L94-97 |
| FR-4 | Reject an operation whose source account is not present in accounts.dat. | bank.cob L128-132 |
| FR-5 | Reject a transfer whose destination is missing or equals the source. | bank.cob L105-108, L128-132 |
| FR-6 | Reject any non-deposit (W, T) whose amount exceeds the source balance. | bank.cob L116-118 |
| FR-7 | Persist resulting balances back to accounts.dat. | bank.cob L133-171 |
| FR-8 | Emit PROCESSED, REJECTED, and TOTAL_CENTS on stdout, zero-padded 8/8/16. | bank.cob L84-86 |
| FR-9 | For identical inputs, produce byte-identical accounts.dat and identical counts to legacy. | bank.cob semantics |
| FR-10 | Keep the on-disk record layout unchanged (fixed-width-compatible). | bank.cob L2-10, L34-48 |
| ID | Requirement | Rationale |
|---|---|---|
| NFR-1 | Batch time is O(accounts + operations); no per-operation full-file scan. | Removes the bank.cob L108 / L133 bottleneck. |
| NFR-2 | At most one write of accounts.dat per run; no temp-file shuffle. | Reduce I/O churn. |
| NFR-3 | Runs on Python 3 standard library only. | Portability, easy hosting. |
| NFR-4 | Malformed rows are rejected and processing continues (no whole-batch abort). | Match legacy tolerance; met — bank.py L23-25, AT-11. |
| NFR-5 | Behaviour is continuously verifiable by automated tests. | scripts/test_bank.py (legacy/parity) + tests/test_modern.py (engine) + scripts/benchmark.py. |
T=$(mktemp -d)
printf '%s\n' '00000001|000000000100' '00000002|000000000100' > "$T/accounts.dat"
printf '%s\n' \
'D|00000001|00000000|000000000050' \
'W|00000001|00000000|000000000020' \
'T|00000002|00000001|000000000030' \
'W|00000001|00000000|000000099999' \
'T|00000001|00000001|000000000001' \
'Z|00000001|00000000|000000000001' \
'D|00000009|00000000|000000000001' > "$T/operations.dat"
python3 modern/bank.py "$T"
cat "$T/accounts.dat"Observed 2026-09-23:
PROCESSED=00000003
REJECTED=00000004
TOTAL_CENTS=0000000000000230
00000001|000000000160
00000002|000000000070| ID | Covers | Given → When → Then | Observed 2026-09-23 | Status | |
|---|---|---|---|---|---|
| AT-1 | FR-1, FR-7 | acct1=100; D acct1 50 → acct1=150 | acct1 advanced 100→150 within run | ✅ | |
| AT-2 | FR-1, FR-7 | acct1=150; W acct1 20 → acct1=130 | applied; no rejection | ✅ | |
| AT-3 | FR-1, FR-7 | T acct2→acct1 30 → acct2:100→70, acct1:130→160 | final acct1=160, acct2=70 | ✅ | |
| AT-4 | FR-6 | W acct1 99999 with 160 available → rejected | counted in REJECTED=4 | ✅ | |
| AT-5 | FR-5 | T acct1→acct1 1 → rejected (self) | counted in REJECTED=4 | ✅ | |
| AT-6 | FR-2 | Z acct1 1 (bad kind) → rejected | counted in REJECTED=4 | ✅ | |
| AT-7 | FR-4, FR-5 | D acct9 1 (unknown source) → rejected | counted in REJECTED=4 | ✅ | |
| AT-8 | FR-8 | stdout zero-padded 8/8/16 | ...00000003 / ...00000004 / 0000000000000230 | ✅ | |
| AT-9 | FR-7, FR-10 | resulting accounts.dat layout unchanged | `00000001\ | 000000000160 (+acct2`) | ✅ |
| AT-10 | FR-8 | TOTAL_CENTS = sum of balances | 160+70 = 230 = 0000000000000230 | ✅ | |
| AT-11 | FR-3, NFR-4 | amount ABCDEFGHIJKL → reject & continue | rejected; batch continued (bank.py L23-25); verified 2026-09-23 | ✅ | |
| AT-12 | FR-9 | legacy vs modern on identical input → identical output | parity YES, byte-identical accounts.dat in all scripts/evidence/benchmark-*.txt; verified 2026-09-23 | ✅ | |
| AT-13 | NFR-1 | speedup grows with account count (linear modern vs quadratic legacy) | sweep 300→4.3x, 600→8.0x, 1200→13.1x, 2400→24.6x, all parity ok (benchmark-sweep.txt) | ✅ |
Expected counts cross-check: 3 accepted (D, W, T) and 4 rejected (insufficient, self, bad-kind, unknown-source) ⇒ PROCESSED=3, REJECTED=4. ✔
Automated coverage (2026-09-23). python3 tests/test_modern.py → Ran 5 tests … OK:
| Test | Covers |
|---|---|
test_deposit_withdrawal_and_transfer_use_integer_cents | AT-1, AT-2, AT-3, AT-8 |
test_malformed_operations_are_rejected_and_batch_continues | AT-11 |
test_overdraft_unknown_recipient_and_self_transfer_are_rejected | AT-4, AT-5, AT-7 |
test_balance_overflow_is_rejected_without_widening_ledger_record | Safety divergence: 12-digit overflow rejection (see 02-before-after.md §4.3) |
test_duplicate_accounts_fail_before_any_write | Safety divergence: duplicate-ID rejection |
Plus scripts/test_bank.py → Ran 33 tests … OK (with the isolated cobc): fixture generator and metrics-parser units, legacy contract tests, legacy/modern parity tests on byte-identical fixtures, characterization tests for documented divergences (including duplicate IDs and 12-digit overflow), and an end-to-end benchmark.py integration test.
Run them aspython3 tests/test_modern.pyandGNUBOL_PREFIX=/tmp/gcb-build/install python3 scripts/test_bank.py. The demo site (site/tests/, 50 tests) and the operator terminal (legacy-ui/tests/test_terminal.py, 20 tests) run separately.
# With the isolated GnuCOBOL 3.2.0 built by scripts/get_cobc.sh. Compiles legacy/bank.cob,
# generates identical fixtures for both programs, and asserts identical stdout +
# byte-identical accounts.dat before reporting any speedup.
GNUBOL_PREFIX=/tmp/gcb-build/install python3 scripts/benchmark.py --accounts 1200 --operations 400benchmark.py computes a parity_ok gate and refuses to report unless the two engines agree.benchmark.py prints the speedup only after the parity gate passes.GET /api/benchmark, which reports the legacy side as unavailable and speedup: null when cobc is missing (never estimates).
scripts/evidence/benchmark-1200x400.txt (median 1.003951 s → 0.035133 s = 28.6x) and benchmark-5000x500.txt (median 4.727858 s → 0.036914 s = 128.1x). Disclosure: the fixtures are synthetic and the legacy design is deliberately inefficient (whole-file rewrite per operation); these are not general claims about COBOL. See 02-before-after.md §6.
A requirement is done when its AT passes and has a saved transcript. Currently: AT-1…AT-13 all pass — AT-1…AT-11 via the fixture and the 5 tests/test_modern.py cases, AT-12/AT-13 via the byte-identical parity runs and the scaling sweep, plus 33 scripts/test_bank.py tests. The demo site (site/tests/, 50) and terminal (legacy-ui/tests/, 20) suites pass independently. The documented safety divergence — modern rejects duplicate account IDs and 12-digit balance overflow while legacy rewrites duplicate rows and truncates the overflow — is intentional and covered by tests (see 02-before-after.md §4.3). The remaining caveat is operational, not correctness: these were run locally with the isolated compiler, not yet against the public hosted prototype (no https://bbs-sg-bank-demo.pages.dev).
tests/__init__.py (or a pytest wrapper) so both suites run via one command.accounts.dat parsing (bank.py L13) to close the remaining robustness gap.