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

eras.test.ts

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`a71096e6` 2026-06-18 Pavel Safronov	1	import { describe, it, expect } from 'vitest';
	2	import { findEras } from './eras';
	3	import type { Era } from '../types';
	4
	5	const colonial: Era = { name: 'Colonial', start: '1750-01-01', end: null, calendar: 'Gregorian' };
	6	const preColonial: Era = { name: 'Pre-Colonial', start: null, end: '1750-01-01', calendar: 'Algonquian lunar calendar' };
	7	// Deliberately overlaps both of the above around the 1750 boundary.
	8	const transitional: Era = { name: 'Transitional', start: '1700-01-01', end: '1800-01-01', calendar: 'Julian' };
	9
	10	const eras = [colonial, preColonial, transitional];
	11	const names = (date: { year: number; month: number; day: number }) =>
	12	findEras(date, eras).map((e) => e.name);
	13
	14	describe('findEras', () => {
	15	it('matches an open-past era before the boundary', () => {
	16	expect(names({ year: 1600, month: 6, day: 1 })).toEqual(['Pre-Colonial']);
	17	});
	18
	19	it('matches an open-present era after the boundary', () => {
	20	expect(names({ year: 1900, month: 1, day: 1 })).toEqual(['Colonial']);
	21	});
	22
	23	it('is half-open: the end date belongs to the next era, not the ending one', () => {
	24	// 1750-01-01 is excluded from Pre-Colonial (its exclusive end) but included
	25	// in Colonial (its inclusive start). Transitional (1700..1800) also covers it.
	26	expect(names({ year: 1750, month: 1, day: 1 })).toEqual(['Colonial', 'Transitional']);
	27	});
	28
	29	it('returns all overlapping eras at once', () => {
	30	// 1740 is in both Pre-Colonial (< 1750) and Transitional (1700..1800).
	31	expect(names({ year: 1740, month: 1, day: 1 })).toEqual(['Pre-Colonial', 'Transitional']);
	32	// 1760 is in both Colonial (>= 1750) and Transitional.
	33	expect(names({ year: 1760, month: 1, day: 1 })).toEqual(['Colonial', 'Transitional']);
	34	});
	35
	36	it('returns nothing when no era covers the date', () => {
	37	const bounded: Era[] = [{ name: 'Only', start: '1000-01-01', end: '1100-01-01', calendar: 'Julian' }];
	38	expect(findEras({ year: 1200, month: 1, day: 1 }, bounded)).toEqual([]);
	39	});
	40	});