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FA-58776 / Loan amortization schedules / Open access

Installment due date calendar: month boundary test · case 01

Modified-following due dates roll into the next month.

Verified by executionVariant 1 · 7 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Only year changes trigger the roll-back.

VERIFIED REPAIR

Roll back whenever the roll leaves the original month.

Unsuccessful approach: A greater-than test misses December rolling into January.

Case contract

x = {'first_due': [y, m, d] (d may exceed the month length), 'count', 'roll': 'none'|'following'|'modified_following', 'holidays': ISO dates}. Installment i falls in month m+i on the anchor day d clamped to the month length (later months return to d). Unless roll is 'none', a Saturday, Sunday or holiday rolls forward to the next business day; under modified_following a roll that leaves the month instead rolls back to the previous business day. Return ISO date strings.

Why this case matters

Amortization engines drive borrower statements, payoff quotes and investor remittances; a misplaced rounding step, boundary or ordering rule compounds across hundreds of periods.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json
import datetime
import calendar
N = 1
observations = []
def solve(x):
    y, m, d = x['first_due']
    hol = set(x['holidays'])
    def bad(t):
        return t.weekday() >= 5 or t.isoformat() in hol
    out = []
    for i in range(x['count']):
        mm = m - 1 + i
        yy = y + mm // 12
        mm = mm % 12 + 1
        dd = min(d, calendar.monthrange(yy, mm)[1])
        date = datetime.date(yy, mm, dd)
        adj = date
        if x['roll'] != 'none':
            while bad(adj):
                adj += datetime.timedelta(days=1)
            if x['roll'] == 'modified_following' and adj.year != date.year:
                adj = date
                while bad(adj):
                    adj -= datetime.timedelta(days=1)
        out.append(adj.isoformat())
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression: month boundary test', {'first_due': [2023, 3, 31], 'count': 6, 'roll': 'modified_following', 'holidays': ['2024-03-29']}, ['2023-03-31', '2023-04-28', '2023-05-31', '2023-06-30', '2023-07-31', '2023-08-31']], ['regression: month boundary test, partial-repair probe', {'first_due': [2023, 9, 30], 'count': 13, 'roll': 'modified_following', 'holidays': ['2024-03-29', '2023-12-25']}, ['2023-09-29', '2023-10-30', '2023-11-30', '2023-12-29', '2024-01-30', '2024-02-29', '2024-03-28', '2024-04-30', '2024-05-30', '2024-06-28', '2024-07-30', '2024-08-30', '2024-09-30']], ['control 1', {'first_due': [2023, 9, 1], 'count': 13, 'roll': 'modified_following', 'holidays': ['2024-03-29', '2024-05-31']}, ['2023-09-01', '2023-10-02', '2023-11-01', '2023-12-01', '2024-01-01', '2024-02-01', '2024-03-01', '2024-04-01', '2024-05-01', '2024-06-03', '2024-07-01', '2024-08-01', '2024-09-02']], ['control 2', {'first_due': [2024, 7, 28], 'count': 13, 'roll': 'modified_following', 'holidays': ['2024-12-31', '2024-01-01']}, ['2024-07-29', '2024-08-28', '2024-09-30', '2024-10-28', '2024-11-28', '2024-12-30', '2025-01-28', '2025-02-28', '2025-03-28', '2025-04-28', '2025-05-28', '2025-06-30', '2025-07-28']], ['control 3', {'first_due': [2024, 11, 15], 'count': 6, 'roll': 'modified_following', 'holidays': []}, ['2024-11-15', '2024-12-16', '2025-01-15', '2025-02-17', '2025-03-17', '2025-04-15']], ['control 4', {'first_due': [2024, 2, 5], 'count': 3, 'roll': 'modified_following', 'holidays': ['2024-03-29', '2024-05-31', '2023-12-25']}, ['2024-02-05', '2024-03-05', '2024-04-05']], ['control 5', {'first_due': [2023, 8, 15], 'count': 3, 'roll': 'modified_following', 'holidays': ['2024-02-29', '2023-06-30']}, ['2023-08-15', '2023-09-15', '2023-10-16']]], [['regression: month boundary test', {'first_due': [2023, 7, 30], 'count': 6, 'roll': 'modified_following', 'holidays': ['2024-12-31']}, ['2023-07-31', '2023-08-30', '2023-09-29', '2023-10-30', '2023-11-30', '2023-12-29']], ['control 1', {'first_due': [2024, 9, 5], 'count': 13, 'roll': 'following', 'holidays': []}, ['2024-09-05', '2024-10-07', '2024-11-05', '2024-12-05', '2025-01-06', '2025-02-05', '2025-03-05', '2025-04-07', '2025-05-05', '2025-06-05', '2025-07-07', '2025-08-05', '2025-09-05']], ['control 2', {'first_due': [2023, 4, 5], 'count': 6, 'roll': 'following', 'holidays': ['2024-01-01', '2024-05-31', '2023-06-30']}, ['2023-04-05', '2023-05-05', '2023-06-05', '2023-07-05', '2023-08-07', '2023-09-05']], ['control 3', {'first_due': [2023, 6, 5], 'count': 6, 'roll': 'none', 'holidays': ['2024-01-01']}, ['2023-06-05', '2023-07-05', '2023-08-05', '2023-09-05', '2023-10-05', '2023-11-05']], ['control 4', {'first_due': [2023, 11, 1], 'count': 3, 'roll': 'modified_following', 'holidays': ['2024-12-31', '2023-06-30', '2024-05-31']}, ['2023-11-01', '2023-12-01', '2024-01-01']], ['control 5', {'first_due': [2023, 10, 30], 'count': 13, 'roll': 'following', 'holidays': ['2024-01-01', '2024-12-31']}, ['2023-10-30', '2023-11-30', '2024-01-02', '2024-01-30', '2024-02-29', '2024-04-01', '2024-04-30', '2024-05-30', '2024-07-01', '2024-07-30', '2024-08-30', '2024-09-30', '2024-10-30']], ['control 6', {'first_due': [2023, 5, 5], 'count': 13, 'roll': 'none', 'holidays': ['2023-06-30', '2024-03-29', '2024-02-29']}, ['2023-05-05', '2023-06-05', '2023-07-05', '2023-08-05', '2023-09-05', '2023-10-05', '2023-11-05', '2023-12-05', '2024-01-05', '2024-02-05', '2024-03-05', '2024-04-05', '2024-05-05']]], [['regression: month boundary test', {'first_due': [2024, 11, 30], 'count': 6, 'roll': 'modified_following', 'holidays': ['2023-06-30']}, ['2024-11-29', '2024-12-30', '2025-01-30', '2025-02-28', '2025-03-31', '2025-04-30']], ['regression: month boundary test, partial-repair probe', {'first_due': [2023, 5, 31], 'count': 13, 'roll': 'modified_following', 'holidays': []}, ['2023-05-31', '2023-06-30', '2023-07-31', '2023-08-31', '2023-09-29', '2023-10-31', '2023-11-30', '2023-12-29', '2024-01-31', '2024-02-29', '2024-03-29', '2024-04-30', '2024-05-31']], ['control 1', {'first_due': [2023, 9, 1], 'count': 3, 'roll': 'modified_following', 'holidays': []}, ['2023-09-01', '2023-10-02', '2023-11-01']], ['control 2', {'first_due': [2024, 5, 1], 'count': 13, 'roll': 'none', 'holidays': []}, ['2024-05-01', '2024-06-01', '2024-07-01', '2024-08-01', '2024-09-01', '2024-10-01', '2024-11-01', '2024-12-01', '2025-01-01', '2025-02-01', '2025-03-01', '2025-04-01', '2025-05-01']], ['control 3', {'first_due': [2024, 10, 30], 'count': 3, 'roll': 'following', 'holidays': ['2024-05-31', '2023-06-30', '2024-03-29']}, ['2024-10-30', '2024-12-02', '2024-12-30']], ['control 4', {'first_due': [2023, 8, 30], 'count': 13, 'roll': 'following', 'holidays': []}, ['2023-08-30', '2023-10-02', '2023-10-30', '2023-11-30', '2024-01-01', '2024-01-30', '2024-02-29', '2024-04-01', '2024-04-30', '2024-05-30', '2024-07-01', '2024-07-30', '2024-08-30']], ['control 5', {'first_due': [2023, 3, 15], 'count': 13, 'roll': 'none', 'holidays': []}, ['2023-03-15', '2023-04-15', '2023-05-15', '2023-06-15', '2023-07-15', '2023-08-15', '2023-09-15', '2023-10-15', '2023-11-15', '2023-12-15', '2024-01-15', '2024-02-15', '2024-03-15']]], [['regression: month boundary test', {'first_due': [2024, 4, 30], 'count': 13, 'roll': 'modified_following', 'holidays': ['2024-12-31', '2023-12-25', '2024-05-31']}, ['2024-04-30', '2024-05-30', '2024-06-28', '2024-07-30', '2024-08-30', '2024-09-30', '2024-10-30', '2024-11-29', '2024-12-30', '2025-01-30', '2025-02-28', '2025-03-31', '2025-04-30']], ['regression: month boundary test, partial-repair probe', {'first_due': [2023, 10, 31], 'count': 3, 'roll': 'modified_following', 'holidays': []}, ['2023-10-31', '2023-11-30', '2023-12-29']], ['control 1', {'first_due': [2024, 8, 15], 'count': 6, 'roll': 'modified_following', 'holidays': []}, ['2024-08-15', '2024-09-16', '2024-10-15', '2024-11-15', '2024-12-16', '2025-01-15']], ['control 2', {'first_due': [2023, 10, 30], 'count': 6, 'roll': 'none', 'holidays': ['2024-01-01']}, ['2023-10-30', '2023-11-30', '2023-12-30', '2024-01-30', '2024-02-29', '2024-03-30']], ['control 3', {'first_due': [2023, 8, 1], 'count': 3, 'roll': 'following', 'holidays': []}, ['2023-08-01', '2023-09-01', '2023-10-02']], ['control 4', {'first_due': [2023, 2, 28], 'count': 3, 'roll': 'following', 'holidays': ['2023-12-25', '2024-05-31']}, ['2023-02-28', '2023-03-28', '2023-04-28']], ['control 5', {'first_due': [2024, 9, 28], 'count': 13, 'roll': 'none', 'holidays': ['2023-06-30', '2024-01-01', '2024-05-31']}, ['2024-09-28', '2024-10-28', '2024-11-28', '2024-12-28', '2025-01-28', '2025-02-28', '2025-03-28', '2025-04-28', '2025-05-28', '2025-06-28', '2025-07-28', '2025-08-28', '2025-09-28']]], [['regression: month boundary test', {'first_due': [2023, 6, 30], 'count': 6, 'roll': 'modified_following', 'holidays': []}, ['2023-06-30', '2023-07-31', '2023-08-30', '2023-09-29', '2023-10-30', '2023-11-30']], ['regression: month boundary test, partial-repair probe', {'first_due': [2023, 11, 30], 'count': 3, 'roll': 'modified_following', 'holidays': ['2024-01-01', '2024-12-31', '2023-12-25']}, ['2023-11-30', '2023-12-29', '2024-01-30']], ['control 1', {'first_due': [2024, 1, 29], 'count': 6, 'roll': 'none', 'holidays': []}, ['2024-01-29', '2024-02-29', '2024-03-29', '2024-04-29', '2024-05-29', '2024-06-29']], ['control 2', {'first_due': [2023, 10, 30], 'count': 13, 'roll': 'none', 'holidays': ['2024-01-01', '2024-03-29']}, ['2023-10-30', '2023-11-30', '2023-12-30', '2024-01-30', '2024-02-29', '2024-03-30', '2024-04-30', '2024-05-30', '2024-06-30', '2024-07-30', '2024-08-30', '2024-09-30', '2024-10-30']], ['control 3', {'first_due': [2024, 8, 5], 'count': 3, 'roll': 'modified_following', 'holidays': []}, ['2024-08-05', '2024-09-05', '2024-10-07']], ['control 4', {'first_due': [2024, 9, 30], 'count': 6, 'roll': 'none', 'holidays': ['2024-02-29']}, ['2024-09-30', '2024-10-30', '2024-11-30', '2024-12-30', '2025-01-30', '2025-02-28']], ['control 5', {'first_due': [2023, 10, 28], 'count': 3, 'roll': 'following', 'holidays': ['2024-12-31']}, ['2023-10-30', '2023-11-28', '2023-12-28']]]]
for label, args, expected in fixtures[N-1]:
    try:
        actual = solve(args)
    except Exception as exc:
        actual = 'raised ' + type(exc).__name__
    check(label, actual, expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
regression: month boundary test['2023-03-31', '2023-05-01', '2023-05-31', '2023-06-30', '2023-07-31', '2023-08-31']['2023-03-31', '2023-04-28', '2023-05-31', '2023-06-30', '2023-07-31', '2023-08-31']Failed
regression: month boundary test, partial-repair probe['2023-10-02', '2023-10-30', '2023-11-30', '2023-12-29', '2024-01-30', '2024-02-29', '2024-04-01', '2024-04-30', '2024-05-30', '2024-07-01', '2024-07-30', '2024-08-30', '2024-09-30']['2023-09-29', '2023-10-30', '2023-11-30', '2023-12-29', '2024-01-30', '2024-02-29', '2024-03-28', '2024-04-30', '2024-05-30', '2024-06-28', '2024-07-30', '2024-08-30', '2024-09-30']Failed
control 1['2023-09-01', '2023-10-02', '2023-11-01', '2023-12-01', '2024-01-01', '2024-02-01', '2024-03-01', '2024-04-01', '2024-05-01', '2024-06-03', '2024-07-01', '2024-08-01', '2024-09-02']['2023-09-01', '2023-10-02', '2023-11-01', '2023-12-01', '2024-01-01', '2024-02-01', '2024-03-01', '2024-04-01', '2024-05-01', '2024-06-03', '2024-07-01', '2024-08-01', '2024-09-02']Passed
control 2['2024-07-29', '2024-08-28', '2024-09-30', '2024-10-28', '2024-11-28', '2024-12-30', '2025-01-28', '2025-02-28', '2025-03-28', '2025-04-28', '2025-05-28', '2025-06-30', '2025-07-28']['2024-07-29', '2024-08-28', '2024-09-30', '2024-10-28', '2024-11-28', '2024-12-30', '2025-01-28', '2025-02-28', '2025-03-28', '2025-04-28', '2025-05-28', '2025-06-30', '2025-07-28']Passed
control 3['2024-11-15', '2024-12-16', '2025-01-15', '2025-02-17', '2025-03-17', '2025-04-15']['2024-11-15', '2024-12-16', '2025-01-15', '2025-02-17', '2025-03-17', '2025-04-15']Passed
control 4['2024-02-05', '2024-03-05', '2024-04-05']['2024-02-05', '2024-03-05', '2024-04-05']Passed
control 5['2023-08-15', '2023-09-15', '2023-10-16']['2023-08-15', '2023-09-15', '2023-10-16']Passed

SHA-256 / 43b96854a51189a73aa75e19c81ad16f91661418e6ac7c6c6026d7669120459c

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json
import datetime
import calendar
N = 1
observations = []
def solve(x):
    y, m, d = x['first_due']
    hol = set(x['holidays'])
    def bad(t):
        return t.weekday() >= 5 or t.isoformat() in hol
    out = []
    for i in range(x['count']):
        mm = m - 1 + i
        yy = y + mm // 12
        mm = mm % 12 + 1
        dd = min(d, calendar.monthrange(yy, mm)[1])
        date = datetime.date(yy, mm, dd)
        adj = date
        if x['roll'] != 'none':
            while bad(adj):
                adj += datetime.timedelta(days=1)
            if x['roll'] == 'modified_following' and adj.month > date.month:
                adj = date
                while bad(adj):
                    adj -= datetime.timedelta(days=1)
        out.append(adj.isoformat())
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression: month boundary test', {'first_due': [2023, 3, 31], 'count': 6, 'roll': 'modified_following', 'holidays': ['2024-03-29']}, ['2023-03-31', '2023-04-28', '2023-05-31', '2023-06-30', '2023-07-31', '2023-08-31']], ['regression: month boundary test, partial-repair probe', {'first_due': [2023, 9, 30], 'count': 13, 'roll': 'modified_following', 'holidays': ['2024-03-29', '2023-12-25']}, ['2023-09-29', '2023-10-30', '2023-11-30', '2023-12-29', '2024-01-30', '2024-02-29', '2024-03-28', '2024-04-30', '2024-05-30', '2024-06-28', '2024-07-30', '2024-08-30', '2024-09-30']], ['control 1', {'first_due': [2023, 9, 1], 'count': 13, 'roll': 'modified_following', 'holidays': ['2024-03-29', '2024-05-31']}, ['2023-09-01', '2023-10-02', '2023-11-01', '2023-12-01', '2024-01-01', '2024-02-01', '2024-03-01', '2024-04-01', '2024-05-01', '2024-06-03', '2024-07-01', '2024-08-01', '2024-09-02']], ['control 2', {'first_due': [2024, 7, 28], 'count': 13, 'roll': 'modified_following', 'holidays': ['2024-12-31', '2024-01-01']}, ['2024-07-29', '2024-08-28', '2024-09-30', '2024-10-28', '2024-11-28', '2024-12-30', '2025-01-28', '2025-02-28', '2025-03-28', '2025-04-28', '2025-05-28', '2025-06-30', '2025-07-28']], ['control 3', {'first_due': [2024, 11, 15], 'count': 6, 'roll': 'modified_following', 'holidays': []}, ['2024-11-15', '2024-12-16', '2025-01-15', '2025-02-17', '2025-03-17', '2025-04-15']], ['control 4', {'first_due': [2024, 2, 5], 'count': 3, 'roll': 'modified_following', 'holidays': ['2024-03-29', '2024-05-31', '2023-12-25']}, ['2024-02-05', '2024-03-05', '2024-04-05']], ['control 5', {'first_due': [2023, 8, 15], 'count': 3, 'roll': 'modified_following', 'holidays': ['2024-02-29', '2023-06-30']}, ['2023-08-15', '2023-09-15', '2023-10-16']]], [['regression: month boundary test', {'first_due': [2023, 7, 30], 'count': 6, 'roll': 'modified_following', 'holidays': ['2024-12-31']}, ['2023-07-31', '2023-08-30', '2023-09-29', '2023-10-30', '2023-11-30', '2023-12-29']], ['control 1', {'first_due': [2024, 9, 5], 'count': 13, 'roll': 'following', 'holidays': []}, ['2024-09-05', '2024-10-07', '2024-11-05', '2024-12-05', '2025-01-06', '2025-02-05', '2025-03-05', '2025-04-07', '2025-05-05', '2025-06-05', '2025-07-07', '2025-08-05', '2025-09-05']], ['control 2', {'first_due': [2023, 4, 5], 'count': 6, 'roll': 'following', 'holidays': ['2024-01-01', '2024-05-31', '2023-06-30']}, ['2023-04-05', '2023-05-05', '2023-06-05', '2023-07-05', '2023-08-07', '2023-09-05']], ['control 3', {'first_due': [2023, 6, 5], 'count': 6, 'roll': 'none', 'holidays': ['2024-01-01']}, ['2023-06-05', '2023-07-05', '2023-08-05', '2023-09-05', '2023-10-05', '2023-11-05']], ['control 4', {'first_due': [2023, 11, 1], 'count': 3, 'roll': 'modified_following', 'holidays': ['2024-12-31', '2023-06-30', '2024-05-31']}, ['2023-11-01', '2023-12-01', '2024-01-01']], ['control 5', {'first_due': [2023, 10, 30], 'count': 13, 'roll': 'following', 'holidays': ['2024-01-01', '2024-12-31']}, ['2023-10-30', '2023-11-30', '2024-01-02', '2024-01-30', '2024-02-29', '2024-04-01', '2024-04-30', '2024-05-30', '2024-07-01', '2024-07-30', '2024-08-30', '2024-09-30', '2024-10-30']], ['control 6', {'first_due': [2023, 5, 5], 'count': 13, 'roll': 'none', 'holidays': ['2023-06-30', '2024-03-29', '2024-02-29']}, ['2023-05-05', '2023-06-05', '2023-07-05', '2023-08-05', '2023-09-05', '2023-10-05', '2023-11-05', '2023-12-05', '2024-01-05', '2024-02-05', '2024-03-05', '2024-04-05', '2024-05-05']]], [['regression: month boundary test', {'first_due': [2024, 11, 30], 'count': 6, 'roll': 'modified_following', 'holidays': ['2023-06-30']}, ['2024-11-29', '2024-12-30', '2025-01-30', '2025-02-28', '2025-03-31', '2025-04-30']], ['regression: month boundary test, partial-repair probe', {'first_due': [2023, 5, 31], 'count': 13, 'roll': 'modified_following', 'holidays': []}, ['2023-05-31', '2023-06-30', '2023-07-31', '2023-08-31', '2023-09-29', '2023-10-31', '2023-11-30', '2023-12-29', '2024-01-31', '2024-02-29', '2024-03-29', '2024-04-30', '2024-05-31']], ['control 1', {'first_due': [2023, 9, 1], 'count': 3, 'roll': 'modified_following', 'holidays': []}, ['2023-09-01', '2023-10-02', '2023-11-01']], ['control 2', {'first_due': [2024, 5, 1], 'count': 13, 'roll': 'none', 'holidays': []}, ['2024-05-01', '2024-06-01', '2024-07-01', '2024-08-01', '2024-09-01', '2024-10-01', '2024-11-01', '2024-12-01', '2025-01-01', '2025-02-01', '2025-03-01', '2025-04-01', '2025-05-01']], ['control 3', {'first_due': [2024, 10, 30], 'count': 3, 'roll': 'following', 'holidays': ['2024-05-31', '2023-06-30', '2024-03-29']}, ['2024-10-30', '2024-12-02', '2024-12-30']], ['control 4', {'first_due': [2023, 8, 30], 'count': 13, 'roll': 'following', 'holidays': []}, ['2023-08-30', '2023-10-02', '2023-10-30', '2023-11-30', '2024-01-01', '2024-01-30', '2024-02-29', '2024-04-01', '2024-04-30', '2024-05-30', '2024-07-01', '2024-07-30', '2024-08-30']], ['control 5', {'first_due': [2023, 3, 15], 'count': 13, 'roll': 'none', 'holidays': []}, ['2023-03-15', '2023-04-15', '2023-05-15', '2023-06-15', '2023-07-15', '2023-08-15', '2023-09-15', '2023-10-15', '2023-11-15', '2023-12-15', '2024-01-15', '2024-02-15', '2024-03-15']]], [['regression: month boundary test', {'first_due': [2024, 4, 30], 'count': 13, 'roll': 'modified_following', 'holidays': ['2024-12-31', '2023-12-25', '2024-05-31']}, ['2024-04-30', '2024-05-30', '2024-06-28', '2024-07-30', '2024-08-30', '2024-09-30', '2024-10-30', '2024-11-29', '2024-12-30', '2025-01-30', '2025-02-28', '2025-03-31', '2025-04-30']], ['regression: month boundary test, partial-repair probe', {'first_due': [2023, 10, 31], 'count': 3, 'roll': 'modified_following', 'holidays': []}, ['2023-10-31', '2023-11-30', '2023-12-29']], ['control 1', {'first_due': [2024, 8, 15], 'count': 6, 'roll': 'modified_following', 'holidays': []}, ['2024-08-15', '2024-09-16', '2024-10-15', '2024-11-15', '2024-12-16', '2025-01-15']], ['control 2', {'first_due': [2023, 10, 30], 'count': 6, 'roll': 'none', 'holidays': ['2024-01-01']}, ['2023-10-30', '2023-11-30', '2023-12-30', '2024-01-30', '2024-02-29', '2024-03-30']], ['control 3', {'first_due': [2023, 8, 1], 'count': 3, 'roll': 'following', 'holidays': []}, ['2023-08-01', '2023-09-01', '2023-10-02']], ['control 4', {'first_due': [2023, 2, 28], 'count': 3, 'roll': 'following', 'holidays': ['2023-12-25', '2024-05-31']}, ['2023-02-28', '2023-03-28', '2023-04-28']], ['control 5', {'first_due': [2024, 9, 28], 'count': 13, 'roll': 'none', 'holidays': ['2023-06-30', '2024-01-01', '2024-05-31']}, ['2024-09-28', '2024-10-28', '2024-11-28', '2024-12-28', '2025-01-28', '2025-02-28', '2025-03-28', '2025-04-28', '2025-05-28', '2025-06-28', '2025-07-28', '2025-08-28', '2025-09-28']]], [['regression: month boundary test', {'first_due': [2023, 6, 30], 'count': 6, 'roll': 'modified_following', 'holidays': []}, ['2023-06-30', '2023-07-31', '2023-08-30', '2023-09-29', '2023-10-30', '2023-11-30']], ['regression: month boundary test, partial-repair probe', {'first_due': [2023, 11, 30], 'count': 3, 'roll': 'modified_following', 'holidays': ['2024-01-01', '2024-12-31', '2023-12-25']}, ['2023-11-30', '2023-12-29', '2024-01-30']], ['control 1', {'first_due': [2024, 1, 29], 'count': 6, 'roll': 'none', 'holidays': []}, ['2024-01-29', '2024-02-29', '2024-03-29', '2024-04-29', '2024-05-29', '2024-06-29']], ['control 2', {'first_due': [2023, 10, 30], 'count': 13, 'roll': 'none', 'holidays': ['2024-01-01', '2024-03-29']}, ['2023-10-30', '2023-11-30', '2023-12-30', '2024-01-30', '2024-02-29', '2024-03-30', '2024-04-30', '2024-05-30', '2024-06-30', '2024-07-30', '2024-08-30', '2024-09-30', '2024-10-30']], ['control 3', {'first_due': [2024, 8, 5], 'count': 3, 'roll': 'modified_following', 'holidays': []}, ['2024-08-05', '2024-09-05', '2024-10-07']], ['control 4', {'first_due': [2024, 9, 30], 'count': 6, 'roll': 'none', 'holidays': ['2024-02-29']}, ['2024-09-30', '2024-10-30', '2024-11-30', '2024-12-30', '2025-01-30', '2025-02-28']], ['control 5', {'first_due': [2023, 10, 28], 'count': 3, 'roll': 'following', 'holidays': ['2024-12-31']}, ['2023-10-30', '2023-11-28', '2023-12-28']]]]
for label, args, expected in fixtures[N-1]:
    try:
        actual = solve(args)
    except Exception as exc:
        actual = 'raised ' + type(exc).__name__
    check(label, actual, expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
regression: month boundary test['2023-03-31', '2023-04-28', '2023-05-31', '2023-06-30', '2023-07-31', '2023-08-31']['2023-03-31', '2023-04-28', '2023-05-31', '2023-06-30', '2023-07-31', '2023-08-31']Passed
regression: month boundary test, partial-repair probe['2023-09-29', '2023-10-30', '2023-11-30', '2024-01-01', '2024-01-30', '2024-02-29', '2024-03-28', '2024-04-30', '2024-05-30', '2024-06-28', '2024-07-30', '2024-08-30', '2024-09-30']['2023-09-29', '2023-10-30', '2023-11-30', '2023-12-29', '2024-01-30', '2024-02-29', '2024-03-28', '2024-04-30', '2024-05-30', '2024-06-28', '2024-07-30', '2024-08-30', '2024-09-30']Failed
control 1['2023-09-01', '2023-10-02', '2023-11-01', '2023-12-01', '2024-01-01', '2024-02-01', '2024-03-01', '2024-04-01', '2024-05-01', '2024-06-03', '2024-07-01', '2024-08-01', '2024-09-02']['2023-09-01', '2023-10-02', '2023-11-01', '2023-12-01', '2024-01-01', '2024-02-01', '2024-03-01', '2024-04-01', '2024-05-01', '2024-06-03', '2024-07-01', '2024-08-01', '2024-09-02']Passed
control 2['2024-07-29', '2024-08-28', '2024-09-30', '2024-10-28', '2024-11-28', '2024-12-30', '2025-01-28', '2025-02-28', '2025-03-28', '2025-04-28', '2025-05-28', '2025-06-30', '2025-07-28']['2024-07-29', '2024-08-28', '2024-09-30', '2024-10-28', '2024-11-28', '2024-12-30', '2025-01-28', '2025-02-28', '2025-03-28', '2025-04-28', '2025-05-28', '2025-06-30', '2025-07-28']Passed
control 3['2024-11-15', '2024-12-16', '2025-01-15', '2025-02-17', '2025-03-17', '2025-04-15']['2024-11-15', '2024-12-16', '2025-01-15', '2025-02-17', '2025-03-17', '2025-04-15']Passed
control 4['2024-02-05', '2024-03-05', '2024-04-05']['2024-02-05', '2024-03-05', '2024-04-05']Passed
control 5['2023-08-15', '2023-09-15', '2023-10-16']['2023-08-15', '2023-09-15', '2023-10-16']Passed

SHA-256 / e883e67cebffd23582d3fcf8d48af7601d3a9e1dee3d9a052ed397e82faf1ef6

3 / The verified repair

Exit 0
"""Failure Map reference implementation. Python standard library only."""
import json
import datetime
import calendar
N = 1
observations = []
def solve(x):
    y, m, d = x['first_due']
    hol = set(x['holidays'])
    def bad(t):
        return t.weekday() >= 5 or t.isoformat() in hol
    out = []
    for i in range(x['count']):
        mm = m - 1 + i
        yy = y + mm // 12
        mm = mm % 12 + 1
        dd = min(d, calendar.monthrange(yy, mm)[1])
        date = datetime.date(yy, mm, dd)
        adj = date
        if x['roll'] != 'none':
            while bad(adj):
                adj += datetime.timedelta(days=1)
            if x['roll'] == 'modified_following' and adj.month != date.month:
                adj = date
                while bad(adj):
                    adj -= datetime.timedelta(days=1)
        out.append(adj.isoformat())
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression: month boundary test', {'first_due': [2023, 3, 31], 'count': 6, 'roll': 'modified_following', 'holidays': ['2024-03-29']}, ['2023-03-31', '2023-04-28', '2023-05-31', '2023-06-30', '2023-07-31', '2023-08-31']], ['regression: month boundary test, partial-repair probe', {'first_due': [2023, 9, 30], 'count': 13, 'roll': 'modified_following', 'holidays': ['2024-03-29', '2023-12-25']}, ['2023-09-29', '2023-10-30', '2023-11-30', '2023-12-29', '2024-01-30', '2024-02-29', '2024-03-28', '2024-04-30', '2024-05-30', '2024-06-28', '2024-07-30', '2024-08-30', '2024-09-30']], ['control 1', {'first_due': [2023, 9, 1], 'count': 13, 'roll': 'modified_following', 'holidays': ['2024-03-29', '2024-05-31']}, ['2023-09-01', '2023-10-02', '2023-11-01', '2023-12-01', '2024-01-01', '2024-02-01', '2024-03-01', '2024-04-01', '2024-05-01', '2024-06-03', '2024-07-01', '2024-08-01', '2024-09-02']], ['control 2', {'first_due': [2024, 7, 28], 'count': 13, 'roll': 'modified_following', 'holidays': ['2024-12-31', '2024-01-01']}, ['2024-07-29', '2024-08-28', '2024-09-30', '2024-10-28', '2024-11-28', '2024-12-30', '2025-01-28', '2025-02-28', '2025-03-28', '2025-04-28', '2025-05-28', '2025-06-30', '2025-07-28']], ['control 3', {'first_due': [2024, 11, 15], 'count': 6, 'roll': 'modified_following', 'holidays': []}, ['2024-11-15', '2024-12-16', '2025-01-15', '2025-02-17', '2025-03-17', '2025-04-15']], ['control 4', {'first_due': [2024, 2, 5], 'count': 3, 'roll': 'modified_following', 'holidays': ['2024-03-29', '2024-05-31', '2023-12-25']}, ['2024-02-05', '2024-03-05', '2024-04-05']], ['control 5', {'first_due': [2023, 8, 15], 'count': 3, 'roll': 'modified_following', 'holidays': ['2024-02-29', '2023-06-30']}, ['2023-08-15', '2023-09-15', '2023-10-16']]], [['regression: month boundary test', {'first_due': [2023, 7, 30], 'count': 6, 'roll': 'modified_following', 'holidays': ['2024-12-31']}, ['2023-07-31', '2023-08-30', '2023-09-29', '2023-10-30', '2023-11-30', '2023-12-29']], ['control 1', {'first_due': [2024, 9, 5], 'count': 13, 'roll': 'following', 'holidays': []}, ['2024-09-05', '2024-10-07', '2024-11-05', '2024-12-05', '2025-01-06', '2025-02-05', '2025-03-05', '2025-04-07', '2025-05-05', '2025-06-05', '2025-07-07', '2025-08-05', '2025-09-05']], ['control 2', {'first_due': [2023, 4, 5], 'count': 6, 'roll': 'following', 'holidays': ['2024-01-01', '2024-05-31', '2023-06-30']}, ['2023-04-05', '2023-05-05', '2023-06-05', '2023-07-05', '2023-08-07', '2023-09-05']], ['control 3', {'first_due': [2023, 6, 5], 'count': 6, 'roll': 'none', 'holidays': ['2024-01-01']}, ['2023-06-05', '2023-07-05', '2023-08-05', '2023-09-05', '2023-10-05', '2023-11-05']], ['control 4', {'first_due': [2023, 11, 1], 'count': 3, 'roll': 'modified_following', 'holidays': ['2024-12-31', '2023-06-30', '2024-05-31']}, ['2023-11-01', '2023-12-01', '2024-01-01']], ['control 5', {'first_due': [2023, 10, 30], 'count': 13, 'roll': 'following', 'holidays': ['2024-01-01', '2024-12-31']}, ['2023-10-30', '2023-11-30', '2024-01-02', '2024-01-30', '2024-02-29', '2024-04-01', '2024-04-30', '2024-05-30', '2024-07-01', '2024-07-30', '2024-08-30', '2024-09-30', '2024-10-30']], ['control 6', {'first_due': [2023, 5, 5], 'count': 13, 'roll': 'none', 'holidays': ['2023-06-30', '2024-03-29', '2024-02-29']}, ['2023-05-05', '2023-06-05', '2023-07-05', '2023-08-05', '2023-09-05', '2023-10-05', '2023-11-05', '2023-12-05', '2024-01-05', '2024-02-05', '2024-03-05', '2024-04-05', '2024-05-05']]], [['regression: month boundary test', {'first_due': [2024, 11, 30], 'count': 6, 'roll': 'modified_following', 'holidays': ['2023-06-30']}, ['2024-11-29', '2024-12-30', '2025-01-30', '2025-02-28', '2025-03-31', '2025-04-30']], ['regression: month boundary test, partial-repair probe', {'first_due': [2023, 5, 31], 'count': 13, 'roll': 'modified_following', 'holidays': []}, ['2023-05-31', '2023-06-30', '2023-07-31', '2023-08-31', '2023-09-29', '2023-10-31', '2023-11-30', '2023-12-29', '2024-01-31', '2024-02-29', '2024-03-29', '2024-04-30', '2024-05-31']], ['control 1', {'first_due': [2023, 9, 1], 'count': 3, 'roll': 'modified_following', 'holidays': []}, ['2023-09-01', '2023-10-02', '2023-11-01']], ['control 2', {'first_due': [2024, 5, 1], 'count': 13, 'roll': 'none', 'holidays': []}, ['2024-05-01', '2024-06-01', '2024-07-01', '2024-08-01', '2024-09-01', '2024-10-01', '2024-11-01', '2024-12-01', '2025-01-01', '2025-02-01', '2025-03-01', '2025-04-01', '2025-05-01']], ['control 3', {'first_due': [2024, 10, 30], 'count': 3, 'roll': 'following', 'holidays': ['2024-05-31', '2023-06-30', '2024-03-29']}, ['2024-10-30', '2024-12-02', '2024-12-30']], ['control 4', {'first_due': [2023, 8, 30], 'count': 13, 'roll': 'following', 'holidays': []}, ['2023-08-30', '2023-10-02', '2023-10-30', '2023-11-30', '2024-01-01', '2024-01-30', '2024-02-29', '2024-04-01', '2024-04-30', '2024-05-30', '2024-07-01', '2024-07-30', '2024-08-30']], ['control 5', {'first_due': [2023, 3, 15], 'count': 13, 'roll': 'none', 'holidays': []}, ['2023-03-15', '2023-04-15', '2023-05-15', '2023-06-15', '2023-07-15', '2023-08-15', '2023-09-15', '2023-10-15', '2023-11-15', '2023-12-15', '2024-01-15', '2024-02-15', '2024-03-15']]], [['regression: month boundary test', {'first_due': [2024, 4, 30], 'count': 13, 'roll': 'modified_following', 'holidays': ['2024-12-31', '2023-12-25', '2024-05-31']}, ['2024-04-30', '2024-05-30', '2024-06-28', '2024-07-30', '2024-08-30', '2024-09-30', '2024-10-30', '2024-11-29', '2024-12-30', '2025-01-30', '2025-02-28', '2025-03-31', '2025-04-30']], ['regression: month boundary test, partial-repair probe', {'first_due': [2023, 10, 31], 'count': 3, 'roll': 'modified_following', 'holidays': []}, ['2023-10-31', '2023-11-30', '2023-12-29']], ['control 1', {'first_due': [2024, 8, 15], 'count': 6, 'roll': 'modified_following', 'holidays': []}, ['2024-08-15', '2024-09-16', '2024-10-15', '2024-11-15', '2024-12-16', '2025-01-15']], ['control 2', {'first_due': [2023, 10, 30], 'count': 6, 'roll': 'none', 'holidays': ['2024-01-01']}, ['2023-10-30', '2023-11-30', '2023-12-30', '2024-01-30', '2024-02-29', '2024-03-30']], ['control 3', {'first_due': [2023, 8, 1], 'count': 3, 'roll': 'following', 'holidays': []}, ['2023-08-01', '2023-09-01', '2023-10-02']], ['control 4', {'first_due': [2023, 2, 28], 'count': 3, 'roll': 'following', 'holidays': ['2023-12-25', '2024-05-31']}, ['2023-02-28', '2023-03-28', '2023-04-28']], ['control 5', {'first_due': [2024, 9, 28], 'count': 13, 'roll': 'none', 'holidays': ['2023-06-30', '2024-01-01', '2024-05-31']}, ['2024-09-28', '2024-10-28', '2024-11-28', '2024-12-28', '2025-01-28', '2025-02-28', '2025-03-28', '2025-04-28', '2025-05-28', '2025-06-28', '2025-07-28', '2025-08-28', '2025-09-28']]], [['regression: month boundary test', {'first_due': [2023, 6, 30], 'count': 6, 'roll': 'modified_following', 'holidays': []}, ['2023-06-30', '2023-07-31', '2023-08-30', '2023-09-29', '2023-10-30', '2023-11-30']], ['regression: month boundary test, partial-repair probe', {'first_due': [2023, 11, 30], 'count': 3, 'roll': 'modified_following', 'holidays': ['2024-01-01', '2024-12-31', '2023-12-25']}, ['2023-11-30', '2023-12-29', '2024-01-30']], ['control 1', {'first_due': [2024, 1, 29], 'count': 6, 'roll': 'none', 'holidays': []}, ['2024-01-29', '2024-02-29', '2024-03-29', '2024-04-29', '2024-05-29', '2024-06-29']], ['control 2', {'first_due': [2023, 10, 30], 'count': 13, 'roll': 'none', 'holidays': ['2024-01-01', '2024-03-29']}, ['2023-10-30', '2023-11-30', '2023-12-30', '2024-01-30', '2024-02-29', '2024-03-30', '2024-04-30', '2024-05-30', '2024-06-30', '2024-07-30', '2024-08-30', '2024-09-30', '2024-10-30']], ['control 3', {'first_due': [2024, 8, 5], 'count': 3, 'roll': 'modified_following', 'holidays': []}, ['2024-08-05', '2024-09-05', '2024-10-07']], ['control 4', {'first_due': [2024, 9, 30], 'count': 6, 'roll': 'none', 'holidays': ['2024-02-29']}, ['2024-09-30', '2024-10-30', '2024-11-30', '2024-12-30', '2025-01-30', '2025-02-28']], ['control 5', {'first_due': [2023, 10, 28], 'count': 3, 'roll': 'following', 'holidays': ['2024-12-31']}, ['2023-10-30', '2023-11-28', '2023-12-28']]]]
for label, args, expected in fixtures[N-1]:
    try:
        actual = solve(args)
    except Exception as exc:
        actual = 'raised ' + type(exc).__name__
    check(label, actual, expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
regression: month boundary test['2023-03-31', '2023-04-28', '2023-05-31', '2023-06-30', '2023-07-31', '2023-08-31']['2023-03-31', '2023-04-28', '2023-05-31', '2023-06-30', '2023-07-31', '2023-08-31']Passed
regression: month boundary test, partial-repair probe['2023-09-29', '2023-10-30', '2023-11-30', '2023-12-29', '2024-01-30', '2024-02-29', '2024-03-28', '2024-04-30', '2024-05-30', '2024-06-28', '2024-07-30', '2024-08-30', '2024-09-30']['2023-09-29', '2023-10-30', '2023-11-30', '2023-12-29', '2024-01-30', '2024-02-29', '2024-03-28', '2024-04-30', '2024-05-30', '2024-06-28', '2024-07-30', '2024-08-30', '2024-09-30']Passed
control 1['2023-09-01', '2023-10-02', '2023-11-01', '2023-12-01', '2024-01-01', '2024-02-01', '2024-03-01', '2024-04-01', '2024-05-01', '2024-06-03', '2024-07-01', '2024-08-01', '2024-09-02']['2023-09-01', '2023-10-02', '2023-11-01', '2023-12-01', '2024-01-01', '2024-02-01', '2024-03-01', '2024-04-01', '2024-05-01', '2024-06-03', '2024-07-01', '2024-08-01', '2024-09-02']Passed
control 2['2024-07-29', '2024-08-28', '2024-09-30', '2024-10-28', '2024-11-28', '2024-12-30', '2025-01-28', '2025-02-28', '2025-03-28', '2025-04-28', '2025-05-28', '2025-06-30', '2025-07-28']['2024-07-29', '2024-08-28', '2024-09-30', '2024-10-28', '2024-11-28', '2024-12-30', '2025-01-28', '2025-02-28', '2025-03-28', '2025-04-28', '2025-05-28', '2025-06-30', '2025-07-28']Passed
control 3['2024-11-15', '2024-12-16', '2025-01-15', '2025-02-17', '2025-03-17', '2025-04-15']['2024-11-15', '2024-12-16', '2025-01-15', '2025-02-17', '2025-03-17', '2025-04-15']Passed
control 4['2024-02-05', '2024-03-05', '2024-04-05']['2024-02-05', '2024-03-05', '2024-04-05']Passed
control 5['2023-08-15', '2023-09-15', '2023-10-16']['2023-08-15', '2023-09-15', '2023-10-16']Passed

SHA-256 / 3275f912b58b679f1078f9b90c39780c95a2052b76af5eb11173e46decef6c2c

Verification & scope

A deterministic bounded teaching model with stipulated toy lending rules stated in the contract; money is integer cents and rates are basis points; it makes no claim of conformance to any regulation, servicing standard or product. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:46:29.988806+00:00.

Case digest / f488a47dc59cae37bb70a10297c310ec21c555fc1650524b67b09521e8e6ed1e