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

VariantJS common functions and utilities

import getLastDayOfPrevMonth from '../../dates/getLastDayOfPrevMonth';

describe('getLastDayOfPrevMonth', () => {
  it('gets the last day of prev month if is first month', () => {
    // 2020-01-15
    const date = new Date(2020, 0, 15);

    expect(getLastDayOfPrevMonth(date)).toEqual(new Date(2019, 11, 31));
  });

  it('gets the last day of prev month if has 29 days', () => {
    // 2020-03-15
    const date = new Date(2020, 2, 15);

    expect(getLastDayOfPrevMonth(date)).toEqual(new Date(2020, 1, 29));
  });

  it('gets the last day of prev month if has 30 days', () => {
    // 2020-07-15
    const date = new Date(2020, 6, 15);

    expect(getLastDayOfPrevMonth(date)).toEqual(new Date(2020, 5, 30));
  });

  it('doesnt affects the original date', () => {
    const originalDate = new Date(2020, 0, 15, 10, 11, 12);
    const date = new Date(2020, 0, 15, 10, 11, 12);

    getLastDayOfPrevMonth(date);

    expect(date).toEqual(originalDate);
  });

  it('works with dates before 1970', () => {
    const date = new Date('0010-02-18T00:00:00.000Z');
    const expected = new Date('0010-01-31T00:00:00.000Z');
    
    expect(getLastDayOfPrevMonth(date)).toEqual(expected);
  });
});