@variantjs/core/src/__tests__/dates/addYears.test.ts

VariantJS common functions and utilities

import addYears from '../../dates/addYears';

describe('addYears', () => {
  it('adds 1 year by default', () => {
    const date = new Date(2020, 0, 15);
    const expected = new Date(2021, 0, 15);

    expect(addYears(date)).toEqual(expected);
  });

  it('adds a year to a date before 1970', () => {
    const date = new Date('0010-02-18T12:00:00.000Z');
    const expected = new Date('0011-02-18T12:00:00.000Z');
    
    expect(addYears(date)).toEqual(expected);
  });

  it('uses the last day of same month if doesnt have an equivalent', () => {
    const date = new Date(2024, 1, 29);
    const expected = new Date(2025, 1, 28);

    expect(addYears(date)).toEqual(expected);
  });

  it('accepts a custom amount of years', () => {
    const date = new Date(2020, 0, 15);
    const expected = new Date(2023, 0, 15);

    expect(addYears(date, 3)).toEqual(expected);
  });

  it('accepts a negative amount of years', () => {
    const date = new Date(2020, 0, 15);
    const expected = new Date(2017, 0, 15);

    expect(addYears(date, -3)).toEqual(expected);
  });

  it('doesnt affect the original date', () => {
    const date = new Date(2020, 0, 15);

    expect(date).toEqual(new Date(2020, 0, 15));
  });
});