when-am-i / files / src / utils / historicalDate.test.ts

historicalDate.test.ts

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`34c4dd59` 2026-06-18 Pavel Safronov	1	import { describe, it, expect } from 'vitest';
`4014e5e0` 2026-06-18 Pavel Safronov	2	import {
	3	daysInMonth,
	4	daysInYear,
	5	dayOfYear,
	6	fromDayOfYear,
	7	toHistoricalDate,
	8	fromHistoricalDate,
	9	clampDay,
	10	} from './historicalDate';
`34c4dd59` 2026-06-18 Pavel Safronov	11
	12	describe('daysInMonth', () => {
	13	it('handles February leap years (Gregorian rule)', () => {
	14	expect(daysInMonth(2000, 2)).toBe(29); // divisible by 400
	15	expect(daysInMonth(1900, 2)).toBe(28); // divisible by 100, not 400
	16	expect(daysInMonth(2004, 2)).toBe(29);
	17	expect(daysInMonth(2001, 2)).toBe(28);
	18	});
	19
	20	it('handles 30- and 31-day months', () => {
	21	expect(daysInMonth(2026, 4)).toBe(30);
	22	expect(daysInMonth(2026, 12)).toBe(31);
	23	});
	24	});
	25
`4014e5e0` 2026-06-18 Pavel Safronov	26	describe('day-of-year helpers', () => {
	27	it('daysInYear handles leap years', () => {
	28	expect(daysInYear(2000)).toBe(366);
	29	expect(daysInYear(1900)).toBe(365);
	30	expect(daysInYear(2001)).toBe(365);
	31	});
	32
	33	it('dayOfYear counts from Jan 1', () => {
	34	expect(dayOfYear(2001, 1, 1)).toBe(1);
	35	expect(dayOfYear(2001, 3, 1)).toBe(60); // 31 + 28 + 1
	36	expect(dayOfYear(2000, 3, 1)).toBe(61); // leap: 31 + 29 + 1
	37	expect(dayOfYear(2001, 12, 31)).toBe(365);
	38	});
	39
	40	it('fromDayOfYear inverts dayOfYear', () => {
	41	for (const [year, m, d] of [[2001, 3, 1], [2000, 3, 1], [2026, 6, 18], [1999, 12, 31]] as const) {
	42	expect(fromDayOfYear(year, dayOfYear(year, m, d))).toEqual({ month: m, day: d });
	43	}
	44	});
	45
	46	it('fromDayOfYear clamps out-of-range input', () => {
	47	expect(fromDayOfYear(2001, 999)).toEqual({ month: 12, day: 31 });
	48	expect(fromDayOfYear(2001, 0)).toEqual({ month: 1, day: 1 });
	49	});
	50	});
	51
`34c4dd59` 2026-06-18 Pavel Safronov	52	describe('toHistoricalDate / fromHistoricalDate', () => {
	53	it('passes CE years through unchanged', () => {
	54	expect(toHistoricalDate({ year: 1700, month: 3, day: 22, era: 'CE' })).toEqual({ year: 1700, month: 3, day: 22 });
	55	});
	56
	57	it('maps BCE onto astronomical numbering (1 BCE = 0)', () => {
	58	expect(toHistoricalDate({ year: 1, month: 1, day: 1, era: 'BCE' })).toEqual({ year: 0, month: 1, day: 1 });
	59	expect(toHistoricalDate({ year: 44, month: 3, day: 15, era: 'BCE' })).toEqual({ year: -43, month: 3, day: 15 });
	60	});
	61
	62	it('round-trips both directions', () => {
	63	for (const d of [
	64	{ year: 2026, month: 6, day: 18, era: 'CE' as const },
	65	{ year: 1, month: 1, day: 1, era: 'BCE' as const },
	66	{ year: 44, month: 3, day: 15, era: 'BCE' as const },
	67	]) {
	68	expect(fromHistoricalDate(toHistoricalDate(d))).toEqual(d);
	69	}
	70	});
	71	});
	72
	73	describe('clampDay', () => {
	74	it('clamps a day past the end of the month', () => {
	75	expect(clampDay({ year: 2025, month: 2, day: 31, era: 'CE' })).toMatchObject({ month: 2, day: 28 });
	76	expect(clampDay({ year: 2024, month: 2, day: 31, era: 'CE' })).toMatchObject({ day: 29 });
	77	});
	78
	79	it('leaves a valid day alone', () => {
	80	expect(clampDay({ year: 2026, month: 6, day: 15, era: 'CE' })).toMatchObject({ day: 15 });
	81	});
	82	});