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Monthly day 29-31 with OMIT/BACKWARD/FORWARD skip policy: backward target · case 01

BACKWARD from the 31st lands on the 28th of 30-day months.

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The backward target assumes the shortest month length.

VERIFIED REPAIR

At the backward target decision use `dt.date(y, m, dim)`, leaving the other decision sites of the model unchanged.

Unsuccessful approach: The partial repair `dt.date(y, m, 28 if m == 2 else 30)` hard-codes the 30th and February 28, ignoring leap-year February.

Case contract

FREQ=MONTHLY on a fixed monthday from the dtstart month. When the day does not exist in a month, skip decides: OMIT (also the default when skip is None) drops the month, BACKWARD uses the last day of the month, FORWARD uses the first day of the following month. February has 29 days in leap years. Instances before dtstart are dropped. Return the first count ISO dates.

Why this case matters

Recurring calendar series are expanded into concrete instances for display, reminders and conflict checks.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json
import datetime as dt
import calendar
N = 1
observations = []
def solve(dtstart, monthday, skip, count):
    start = dt.date.fromisoformat(dtstart)
    out = []
    for k in range(240):
        mi = start.month - 1 + k
        y, m = start.year + mi // 12, mi % 12 + 1
        dim = calendar.monthrange(y, m)[1]
        if monthday <= dim:
            d = dt.date(y, m, monthday)
        elif skip in (None, 'OMIT'):
            continue
        elif skip == 'BACKWARD':
            d = dt.date(y, m, 28)
        else:
            d = dt.date(y, m, dim) + dt.timedelta(days=1)
        if d < start:
            continue
        out.append(d.isoformat())
        if len(out) >= count:
            break
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression: 31st forward in common year',
   ['2023-01-31', 31, 'FORWARD', 4],
   ['2023-01-31', '2023-03-01', '2023-03-31', '2023-05-01']),
  ('default omits', ['2023-01-30', 30, None, 3], ['2023-01-30', '2023-03-30', '2023-04-30']),
  ('explicit omit', ['2023-01-31', 31, 'OMIT', 3], ['2023-01-31', '2023-03-31', '2023-05-31']),
  ('backward from 31st',
   ['2024-03-31', 31, 'BACKWARD', 4],
   ['2024-03-31', '2024-04-30', '2024-05-31', '2024-06-30']),
  ('leap february 29', ['2024-01-29', 29, 'BACKWARD', 3], ['2024-01-29', '2024-02-29', '2024-03-29']),
  ('common february 29 backward',
   ['2023-01-29', 29, 'BACKWARD', 3],
   ['2023-01-29', '2023-02-28', '2023-03-29']),
  ('forward 30th in february leap',
   ['2024-01-30', 30, 'FORWARD', 3],
   ['2024-01-30', '2024-03-01', '2024-03-30']),
  ('backward 31st leap february',
   ['2024-01-31', 31, 'BACKWARD', 3],
   ['2024-01-31', '2024-02-29', '2024-03-31'])],
 [('explicit omit', ['2023-01-31', 31, 'OMIT', 3], ['2023-01-31', '2023-03-31', '2023-05-31']),
  ('backward from 31st',
   ['2024-03-31', 31, 'BACKWARD', 4],
   ['2024-03-31', '2024-04-30', '2024-05-31', '2024-06-30']),
  ('leap february 29', ['2024-01-29', 29, 'BACKWARD', 3], ['2024-01-29', '2024-02-29', '2024-03-29']),
  ('common february 29 backward',
   ['2023-01-29', 29, 'BACKWARD', 3],
   ['2023-01-29', '2023-02-28', '2023-03-29']),
  ('forward 30th in february leap',
   ['2024-01-30', 30, 'FORWARD', 3],
   ['2024-01-30', '2024-03-01', '2024-03-30']),
  ('backward 30th in february',
   ['2023-01-30', 30, 'BACKWARD', 3],
   ['2023-01-30', '2023-02-28', '2023-03-30']),
  ('forward 29th in common february',
   ['2023-01-29', 29, 'FORWARD', 3],
   ['2023-01-29', '2023-03-01', '2023-03-29']),
  ('backward 31st leap february',
   ['2024-01-31', 31, 'BACKWARD', 3],
   ['2024-01-31', '2024-02-29', '2024-03-31'])],
 [('leap february 29', ['2024-01-29', 29, 'BACKWARD', 3], ['2024-01-29', '2024-02-29', '2024-03-29']),
  ('common february 29 backward',
   ['2023-01-29', 29, 'BACKWARD', 3],
   ['2023-01-29', '2023-02-28', '2023-03-29']),
  ('forward 30th in february leap',
   ['2024-01-30', 30, 'FORWARD', 3],
   ['2024-01-30', '2024-03-01', '2024-03-30']),
  ('backward 30th in february',
   ['2023-01-30', 30, 'BACKWARD', 3],
   ['2023-01-30', '2023-02-28', '2023-03-30']),
  ('forward 29th in common february',
   ['2023-01-29', 29, 'FORWARD', 3],
   ['2023-01-29', '2023-03-01', '2023-03-29']),
  ('leap day omit', ['2024-01-29', 29, None, 3], ['2024-01-29', '2024-02-29', '2024-03-29']),
  ('forward from april 31', ['2024-04-15', 31, 'FORWARD', 3], ['2024-05-01', '2024-05-31', '2024-07-01']),
  ('backward 31st leap february',
   ['2024-01-31', 31, 'BACKWARD', 3],
   ['2024-01-31', '2024-02-29', '2024-03-31'])],
 [('forward 30th in february leap',
   ['2024-01-30', 30, 'FORWARD', 3],
   ['2024-01-30', '2024-03-01', '2024-03-30']),
  ('backward 30th in february',
   ['2023-01-30', 30, 'BACKWARD', 3],
   ['2023-01-30', '2023-02-28', '2023-03-30']),
  ('forward 29th in common february',
   ['2023-01-29', 29, 'FORWARD', 3],
   ['2023-01-29', '2023-03-01', '2023-03-29']),
  ('leap day omit', ['2024-01-29', 29, None, 3], ['2024-01-29', '2024-02-29', '2024-03-29']),
  ('forward from april 31', ['2024-04-15', 31, 'FORWARD', 3], ['2024-05-01', '2024-05-31', '2024-07-01']),
  ('backward 31st leap february',
   ['2024-01-31', 31, 'BACKWARD', 3],
   ['2024-01-31', '2024-02-29', '2024-03-31']),
  ('century leap day', ['2000-01-29', 29, 'OMIT', 3], ['2000-01-29', '2000-02-29', '2000-03-29'])],
 [('forward 29th in common february',
   ['2023-01-29', 29, 'FORWARD', 3],
   ['2023-01-29', '2023-03-01', '2023-03-29']),
  ('leap day omit', ['2024-01-29', 29, None, 3], ['2024-01-29', '2024-02-29', '2024-03-29']),
  ('forward from april 31', ['2024-04-15', 31, 'FORWARD', 3], ['2024-05-01', '2024-05-31', '2024-07-01']),
  ('backward 31st leap february',
   ['2024-01-31', 31, 'BACKWARD', 3],
   ['2024-01-31', '2024-02-29', '2024-03-31']),
  ('century leap day', ['2000-01-29', 29, 'OMIT', 3], ['2000-01-29', '2000-02-29', '2000-03-29']),
  ('century common february', ['2100-01-29', 29, 'OMIT', 3], ['2100-01-29', '2100-03-29', '2100-04-29']),
  ('regression: 31st forward in common year',
   ['2023-01-31', 31, 'FORWARD', 4],
   ['2023-01-31', '2023-03-01', '2023-03-31', '2023-05-01'])]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), 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: 31st forward in common year['2023-01-31', '2023-03-01', '2023-03-31', '2023-05-01']['2023-01-31', '2023-03-01', '2023-03-31', '2023-05-01']Passed
default omits['2023-01-30', '2023-03-30', '2023-04-30']['2023-01-30', '2023-03-30', '2023-04-30']Passed
explicit omit['2023-01-31', '2023-03-31', '2023-05-31']['2023-01-31', '2023-03-31', '2023-05-31']Passed
backward from 31st['2024-03-31', '2024-04-28', '2024-05-31', '2024-06-28']['2024-03-31', '2024-04-30', '2024-05-31', '2024-06-30']Failed
leap february 29['2024-01-29', '2024-02-29', '2024-03-29']['2024-01-29', '2024-02-29', '2024-03-29']Passed
common february 29 backward['2023-01-29', '2023-02-28', '2023-03-29']['2023-01-29', '2023-02-28', '2023-03-29']Passed
forward 30th in february leap['2024-01-30', '2024-03-01', '2024-03-30']['2024-01-30', '2024-03-01', '2024-03-30']Passed
backward 31st leap february['2024-01-31', '2024-02-28', '2024-03-31']['2024-01-31', '2024-02-29', '2024-03-31']Failed

SHA-256 / f61f5a8f782a434e786572b707bc460438c32a78d71dd2c9af1426faf13b55fb

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json
import datetime as dt
import calendar
N = 1
observations = []
def solve(dtstart, monthday, skip, count):
    start = dt.date.fromisoformat(dtstart)
    out = []
    for k in range(240):
        mi = start.month - 1 + k
        y, m = start.year + mi // 12, mi % 12 + 1
        dim = calendar.monthrange(y, m)[1]
        if monthday <= dim:
            d = dt.date(y, m, monthday)
        elif skip in (None, 'OMIT'):
            continue
        elif skip == 'BACKWARD':
            d = dt.date(y, m, 28 if m == 2 else 30)
        else:
            d = dt.date(y, m, dim) + dt.timedelta(days=1)
        if d < start:
            continue
        out.append(d.isoformat())
        if len(out) >= count:
            break
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression: 31st forward in common year',
   ['2023-01-31', 31, 'FORWARD', 4],
   ['2023-01-31', '2023-03-01', '2023-03-31', '2023-05-01']),
  ('default omits', ['2023-01-30', 30, None, 3], ['2023-01-30', '2023-03-30', '2023-04-30']),
  ('explicit omit', ['2023-01-31', 31, 'OMIT', 3], ['2023-01-31', '2023-03-31', '2023-05-31']),
  ('backward from 31st',
   ['2024-03-31', 31, 'BACKWARD', 4],
   ['2024-03-31', '2024-04-30', '2024-05-31', '2024-06-30']),
  ('leap february 29', ['2024-01-29', 29, 'BACKWARD', 3], ['2024-01-29', '2024-02-29', '2024-03-29']),
  ('common february 29 backward',
   ['2023-01-29', 29, 'BACKWARD', 3],
   ['2023-01-29', '2023-02-28', '2023-03-29']),
  ('forward 30th in february leap',
   ['2024-01-30', 30, 'FORWARD', 3],
   ['2024-01-30', '2024-03-01', '2024-03-30']),
  ('backward 31st leap february',
   ['2024-01-31', 31, 'BACKWARD', 3],
   ['2024-01-31', '2024-02-29', '2024-03-31'])],
 [('explicit omit', ['2023-01-31', 31, 'OMIT', 3], ['2023-01-31', '2023-03-31', '2023-05-31']),
  ('backward from 31st',
   ['2024-03-31', 31, 'BACKWARD', 4],
   ['2024-03-31', '2024-04-30', '2024-05-31', '2024-06-30']),
  ('leap february 29', ['2024-01-29', 29, 'BACKWARD', 3], ['2024-01-29', '2024-02-29', '2024-03-29']),
  ('common february 29 backward',
   ['2023-01-29', 29, 'BACKWARD', 3],
   ['2023-01-29', '2023-02-28', '2023-03-29']),
  ('forward 30th in february leap',
   ['2024-01-30', 30, 'FORWARD', 3],
   ['2024-01-30', '2024-03-01', '2024-03-30']),
  ('backward 30th in february',
   ['2023-01-30', 30, 'BACKWARD', 3],
   ['2023-01-30', '2023-02-28', '2023-03-30']),
  ('forward 29th in common february',
   ['2023-01-29', 29, 'FORWARD', 3],
   ['2023-01-29', '2023-03-01', '2023-03-29']),
  ('backward 31st leap february',
   ['2024-01-31', 31, 'BACKWARD', 3],
   ['2024-01-31', '2024-02-29', '2024-03-31'])],
 [('leap february 29', ['2024-01-29', 29, 'BACKWARD', 3], ['2024-01-29', '2024-02-29', '2024-03-29']),
  ('common february 29 backward',
   ['2023-01-29', 29, 'BACKWARD', 3],
   ['2023-01-29', '2023-02-28', '2023-03-29']),
  ('forward 30th in february leap',
   ['2024-01-30', 30, 'FORWARD', 3],
   ['2024-01-30', '2024-03-01', '2024-03-30']),
  ('backward 30th in february',
   ['2023-01-30', 30, 'BACKWARD', 3],
   ['2023-01-30', '2023-02-28', '2023-03-30']),
  ('forward 29th in common february',
   ['2023-01-29', 29, 'FORWARD', 3],
   ['2023-01-29', '2023-03-01', '2023-03-29']),
  ('leap day omit', ['2024-01-29', 29, None, 3], ['2024-01-29', '2024-02-29', '2024-03-29']),
  ('forward from april 31', ['2024-04-15', 31, 'FORWARD', 3], ['2024-05-01', '2024-05-31', '2024-07-01']),
  ('backward 31st leap february',
   ['2024-01-31', 31, 'BACKWARD', 3],
   ['2024-01-31', '2024-02-29', '2024-03-31'])],
 [('forward 30th in february leap',
   ['2024-01-30', 30, 'FORWARD', 3],
   ['2024-01-30', '2024-03-01', '2024-03-30']),
  ('backward 30th in february',
   ['2023-01-30', 30, 'BACKWARD', 3],
   ['2023-01-30', '2023-02-28', '2023-03-30']),
  ('forward 29th in common february',
   ['2023-01-29', 29, 'FORWARD', 3],
   ['2023-01-29', '2023-03-01', '2023-03-29']),
  ('leap day omit', ['2024-01-29', 29, None, 3], ['2024-01-29', '2024-02-29', '2024-03-29']),
  ('forward from april 31', ['2024-04-15', 31, 'FORWARD', 3], ['2024-05-01', '2024-05-31', '2024-07-01']),
  ('backward 31st leap february',
   ['2024-01-31', 31, 'BACKWARD', 3],
   ['2024-01-31', '2024-02-29', '2024-03-31']),
  ('century leap day', ['2000-01-29', 29, 'OMIT', 3], ['2000-01-29', '2000-02-29', '2000-03-29'])],
 [('forward 29th in common february',
   ['2023-01-29', 29, 'FORWARD', 3],
   ['2023-01-29', '2023-03-01', '2023-03-29']),
  ('leap day omit', ['2024-01-29', 29, None, 3], ['2024-01-29', '2024-02-29', '2024-03-29']),
  ('forward from april 31', ['2024-04-15', 31, 'FORWARD', 3], ['2024-05-01', '2024-05-31', '2024-07-01']),
  ('backward 31st leap february',
   ['2024-01-31', 31, 'BACKWARD', 3],
   ['2024-01-31', '2024-02-29', '2024-03-31']),
  ('century leap day', ['2000-01-29', 29, 'OMIT', 3], ['2000-01-29', '2000-02-29', '2000-03-29']),
  ('century common february', ['2100-01-29', 29, 'OMIT', 3], ['2100-01-29', '2100-03-29', '2100-04-29']),
  ('regression: 31st forward in common year',
   ['2023-01-31', 31, 'FORWARD', 4],
   ['2023-01-31', '2023-03-01', '2023-03-31', '2023-05-01'])]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), 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: 31st forward in common year['2023-01-31', '2023-03-01', '2023-03-31', '2023-05-01']['2023-01-31', '2023-03-01', '2023-03-31', '2023-05-01']Passed
default omits['2023-01-30', '2023-03-30', '2023-04-30']['2023-01-30', '2023-03-30', '2023-04-30']Passed
explicit omit['2023-01-31', '2023-03-31', '2023-05-31']['2023-01-31', '2023-03-31', '2023-05-31']Passed
backward from 31st['2024-03-31', '2024-04-30', '2024-05-31', '2024-06-30']['2024-03-31', '2024-04-30', '2024-05-31', '2024-06-30']Passed
leap february 29['2024-01-29', '2024-02-29', '2024-03-29']['2024-01-29', '2024-02-29', '2024-03-29']Passed
common february 29 backward['2023-01-29', '2023-02-28', '2023-03-29']['2023-01-29', '2023-02-28', '2023-03-29']Passed
forward 30th in february leap['2024-01-30', '2024-03-01', '2024-03-30']['2024-01-30', '2024-03-01', '2024-03-30']Passed
backward 31st leap february['2024-01-31', '2024-02-28', '2024-03-31']['2024-01-31', '2024-02-29', '2024-03-31']Failed

SHA-256 / 5316b55ec041ed08bdc015d57c60f7849870b326c8343450296ecd835ce85b56

3 / The verified repair

Exit 0
"""Failure Map reference implementation. Python standard library only."""
import json
import datetime as dt
import calendar
N = 1
observations = []
def solve(dtstart, monthday, skip, count):
    start = dt.date.fromisoformat(dtstart)
    out = []
    for k in range(240):
        mi = start.month - 1 + k
        y, m = start.year + mi // 12, mi % 12 + 1
        dim = calendar.monthrange(y, m)[1]
        if monthday <= dim:
            d = dt.date(y, m, monthday)
        elif skip in (None, 'OMIT'):
            continue
        elif skip == 'BACKWARD':
            d = dt.date(y, m, dim)
        else:
            d = dt.date(y, m, dim) + dt.timedelta(days=1)
        if d < start:
            continue
        out.append(d.isoformat())
        if len(out) >= count:
            break
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression: 31st forward in common year',
   ['2023-01-31', 31, 'FORWARD', 4],
   ['2023-01-31', '2023-03-01', '2023-03-31', '2023-05-01']),
  ('default omits', ['2023-01-30', 30, None, 3], ['2023-01-30', '2023-03-30', '2023-04-30']),
  ('explicit omit', ['2023-01-31', 31, 'OMIT', 3], ['2023-01-31', '2023-03-31', '2023-05-31']),
  ('backward from 31st',
   ['2024-03-31', 31, 'BACKWARD', 4],
   ['2024-03-31', '2024-04-30', '2024-05-31', '2024-06-30']),
  ('leap february 29', ['2024-01-29', 29, 'BACKWARD', 3], ['2024-01-29', '2024-02-29', '2024-03-29']),
  ('common february 29 backward',
   ['2023-01-29', 29, 'BACKWARD', 3],
   ['2023-01-29', '2023-02-28', '2023-03-29']),
  ('forward 30th in february leap',
   ['2024-01-30', 30, 'FORWARD', 3],
   ['2024-01-30', '2024-03-01', '2024-03-30']),
  ('backward 31st leap february',
   ['2024-01-31', 31, 'BACKWARD', 3],
   ['2024-01-31', '2024-02-29', '2024-03-31'])],
 [('explicit omit', ['2023-01-31', 31, 'OMIT', 3], ['2023-01-31', '2023-03-31', '2023-05-31']),
  ('backward from 31st',
   ['2024-03-31', 31, 'BACKWARD', 4],
   ['2024-03-31', '2024-04-30', '2024-05-31', '2024-06-30']),
  ('leap february 29', ['2024-01-29', 29, 'BACKWARD', 3], ['2024-01-29', '2024-02-29', '2024-03-29']),
  ('common february 29 backward',
   ['2023-01-29', 29, 'BACKWARD', 3],
   ['2023-01-29', '2023-02-28', '2023-03-29']),
  ('forward 30th in february leap',
   ['2024-01-30', 30, 'FORWARD', 3],
   ['2024-01-30', '2024-03-01', '2024-03-30']),
  ('backward 30th in february',
   ['2023-01-30', 30, 'BACKWARD', 3],
   ['2023-01-30', '2023-02-28', '2023-03-30']),
  ('forward 29th in common february',
   ['2023-01-29', 29, 'FORWARD', 3],
   ['2023-01-29', '2023-03-01', '2023-03-29']),
  ('backward 31st leap february',
   ['2024-01-31', 31, 'BACKWARD', 3],
   ['2024-01-31', '2024-02-29', '2024-03-31'])],
 [('leap february 29', ['2024-01-29', 29, 'BACKWARD', 3], ['2024-01-29', '2024-02-29', '2024-03-29']),
  ('common february 29 backward',
   ['2023-01-29', 29, 'BACKWARD', 3],
   ['2023-01-29', '2023-02-28', '2023-03-29']),
  ('forward 30th in february leap',
   ['2024-01-30', 30, 'FORWARD', 3],
   ['2024-01-30', '2024-03-01', '2024-03-30']),
  ('backward 30th in february',
   ['2023-01-30', 30, 'BACKWARD', 3],
   ['2023-01-30', '2023-02-28', '2023-03-30']),
  ('forward 29th in common february',
   ['2023-01-29', 29, 'FORWARD', 3],
   ['2023-01-29', '2023-03-01', '2023-03-29']),
  ('leap day omit', ['2024-01-29', 29, None, 3], ['2024-01-29', '2024-02-29', '2024-03-29']),
  ('forward from april 31', ['2024-04-15', 31, 'FORWARD', 3], ['2024-05-01', '2024-05-31', '2024-07-01']),
  ('backward 31st leap february',
   ['2024-01-31', 31, 'BACKWARD', 3],
   ['2024-01-31', '2024-02-29', '2024-03-31'])],
 [('forward 30th in february leap',
   ['2024-01-30', 30, 'FORWARD', 3],
   ['2024-01-30', '2024-03-01', '2024-03-30']),
  ('backward 30th in february',
   ['2023-01-30', 30, 'BACKWARD', 3],
   ['2023-01-30', '2023-02-28', '2023-03-30']),
  ('forward 29th in common february',
   ['2023-01-29', 29, 'FORWARD', 3],
   ['2023-01-29', '2023-03-01', '2023-03-29']),
  ('leap day omit', ['2024-01-29', 29, None, 3], ['2024-01-29', '2024-02-29', '2024-03-29']),
  ('forward from april 31', ['2024-04-15', 31, 'FORWARD', 3], ['2024-05-01', '2024-05-31', '2024-07-01']),
  ('backward 31st leap february',
   ['2024-01-31', 31, 'BACKWARD', 3],
   ['2024-01-31', '2024-02-29', '2024-03-31']),
  ('century leap day', ['2000-01-29', 29, 'OMIT', 3], ['2000-01-29', '2000-02-29', '2000-03-29'])],
 [('forward 29th in common february',
   ['2023-01-29', 29, 'FORWARD', 3],
   ['2023-01-29', '2023-03-01', '2023-03-29']),
  ('leap day omit', ['2024-01-29', 29, None, 3], ['2024-01-29', '2024-02-29', '2024-03-29']),
  ('forward from april 31', ['2024-04-15', 31, 'FORWARD', 3], ['2024-05-01', '2024-05-31', '2024-07-01']),
  ('backward 31st leap february',
   ['2024-01-31', 31, 'BACKWARD', 3],
   ['2024-01-31', '2024-02-29', '2024-03-31']),
  ('century leap day', ['2000-01-29', 29, 'OMIT', 3], ['2000-01-29', '2000-02-29', '2000-03-29']),
  ('century common february', ['2100-01-29', 29, 'OMIT', 3], ['2100-01-29', '2100-03-29', '2100-04-29']),
  ('regression: 31st forward in common year',
   ['2023-01-31', 31, 'FORWARD', 4],
   ['2023-01-31', '2023-03-01', '2023-03-31', '2023-05-01'])]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), 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: 31st forward in common year['2023-01-31', '2023-03-01', '2023-03-31', '2023-05-01']['2023-01-31', '2023-03-01', '2023-03-31', '2023-05-01']Passed
default omits['2023-01-30', '2023-03-30', '2023-04-30']['2023-01-30', '2023-03-30', '2023-04-30']Passed
explicit omit['2023-01-31', '2023-03-31', '2023-05-31']['2023-01-31', '2023-03-31', '2023-05-31']Passed
backward from 31st['2024-03-31', '2024-04-30', '2024-05-31', '2024-06-30']['2024-03-31', '2024-04-30', '2024-05-31', '2024-06-30']Passed
leap february 29['2024-01-29', '2024-02-29', '2024-03-29']['2024-01-29', '2024-02-29', '2024-03-29']Passed
common february 29 backward['2023-01-29', '2023-02-28', '2023-03-29']['2023-01-29', '2023-02-28', '2023-03-29']Passed
forward 30th in february leap['2024-01-30', '2024-03-01', '2024-03-30']['2024-01-30', '2024-03-01', '2024-03-30']Passed
backward 31st leap february['2024-01-31', '2024-02-29', '2024-03-31']['2024-01-31', '2024-02-29', '2024-03-31']Passed

SHA-256 / 7769b37f10598969670d9ce8f6e91057319743073a24b191bd9887f0788baa14

Verification & scope

Stipulated, bounded recurrence-expansion model evaluated offline on explicit fixtures; it is not a complete iCalendar implementation and makes no claim of standards conformance. 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 2026-09-29T14:49:22.951049+00:00.

Case digest / e00702adb4b64ada6de285d52802c2b0eda69055626ab769ef12f3a3b9c4f4be