[
  { "name": "the epoch itself, 1 January 1970, was a Thursday", "args": ["1970-01-01"], "expect": 4 },
  { "name": "an ordinary Wednesday", "args": ["2026-09-16"], "expect": 3 },
  { "name": "Saturday is 6", "args": ["2026-09-19"], "expect": 6 },
  { "name": "Sunday is 7, not 0", "args": ["2026-09-20"], "expect": 7 },
  { "name": "Monday is 1", "args": ["2026-09-21"], "expect": 1 },
  { "name": "1 January 2000 was a Saturday", "args": ["2000-01-01"], "expect": 6 },
  { "name": "31 December 1999 was a Friday", "args": ["1999-12-31"], "expect": 5 },
  { "name": "1 January 1900 was a Monday, well before the epoch", "args": ["1900-01-01"], "expect": 1 },
  { "name": "the 2024 leap day was a Thursday", "args": ["2024-02-29"], "expect": 4 },
  { "name": "1 March 1900 was a Thursday because 1900 had no leap day", "args": ["1900-03-01"], "expect": 4 },
  { "name": "1 March 2000 was a Wednesday because 2000 did have one", "args": ["2000-03-01"], "expect": 3 },
  { "name": "the first supported date, 1 January 0001, is a Monday", "args": ["0001-01-01"], "expect": 1 },
  { "name": "the last supported date, 31 December 9999, is a Friday", "args": ["9999-12-31"], "expect": 5 },
  { "name": "a slash-separated date is an error, not a guess", "args": ["16/09/2026"], "expectError": "is not an ISO date" },
  { "name": "an unpadded month is an error", "args": ["2026-9-16"], "expectError": "is not an ISO date" },
  { "name": "an empty string is an error", "args": [""], "expectError": "is not an ISO date" },
  { "name": "30 February is not a real date", "args": ["2026-02-30"], "expectError": "is not a real calendar date" },
  { "name": "29 February in a non-leap year is rejected", "args": ["2026-02-29"], "expectError": "is not a real calendar date" },
  { "name": "month 00 is rejected", "args": ["2026-00-10"], "expectError": "is not a real calendar date" },
  { "name": "day 00 is rejected", "args": ["2026-09-00"], "expectError": "is not a real calendar date" }
]