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Validating Locale Internationalization Framework in dayjs

This test suite validates the locale functionality in Day.js, ensuring proper handling of date/time localization and formatting. It verifies both instance-level and global locale settings, along with locale inheritance and fallback behaviors.

Test Coverage Overview

The test suite provides comprehensive coverage of locale-related functionality in Day.js:

Instance and global locale settings
Locale inheritance across operations
Custom locale definitions
Fallback behavior for unsupported locales
Compatibility with Moment.js locale handling

Implementation Analysis

The testing approach uses Jest’s describe/it pattern for organized test grouping. Tests validate locale behavior through constructor options, instance methods, and global settings. The implementation includes direct comparison with Moment.js for compatibility verification.

Technical Details

Key technical components include:

MockDate for consistent date testing
Spanish locale (es) as test example
Format string ‘dddd D, MMMM’ for validation
Instance method testing (.locale(), .format())
Global configuration testing (dayjs.locale())

Best Practices Demonstrated

The test suite exemplifies several testing best practices:

Isolation of tests using beforeEach/afterEach hooks
Immutability verification
Edge case handling for unsupported locales
Consistent test patterns across different locale operations
Clear test descriptions and expectations

iamkun/dayjs

test/locale.test.js

            
import MockDate from 'mockdate'
import moment from 'moment'
import dayjs from '../src'
import es from '../src/locale/es'

beforeEach(() => {
  MockDate.set(new Date())
})

afterEach(() => {
  MockDate.reset()
})

const format = 'dddd D, MMMM'
const NOT_SUPPORTED_LOCALE_STRING = 'not_supported_locale_string'

it('Uses spanish locale through constructor', () => { // not recommend
  expect(dayjs('2018-4-28', { locale: es })
    .format(format))
    .toBe('sábado 28, abril')
})

it('set locale for one instance only', () => {
  expect(dayjs('2018-4-28')
    .format(format))
    .toBe('Saturday 28, April')

  expect(dayjs('2018-4-28')
    .locale(es).format(format))
    .toBe('sábado 28, abril')

  expect(dayjs('2018-4-28')
    .format(format))
    .toBe('Saturday 28, April')
})

it('set global locale', () => {
  dayjs.locale('en')
  expect(dayjs('2018-4-28').format(format))
    .toBe('Saturday 28, April')
  dayjs.locale(es)
  expect(dayjs('2018-4-28').format(format))
    .toBe('sábado 28, abril')
  dayjs.locale('en')
  expect(dayjs('2018-4-28').format(format))
    .toBe('Saturday 28, April')
})

it('get instance locale name', () => {
  expect(dayjs().locale()).toBe('en')
  expect(dayjs().locale()).toBe(moment().locale())
  expect(dayjs().locale('es').locale()).toBe('es')
  expect(dayjs().locale('es').locale()).toBe(moment().locale('es').locale())
  dayjs.locale(es)
  moment.locale('es')
  expect(dayjs().locale()).toBe('es')
  expect(dayjs().locale()).toBe(moment().locale())
})

it('immutable instance locale', () => {
  dayjs.locale('en')
  const origin = dayjs('2018-4-28')
  expect(origin.format(format))
    .toBe('Saturday 28, April')
  expect(origin.locale('es').format(format))
    .toBe('sábado 28, abril')
  const changed = origin.locale('es')
  expect(changed.format(format))
    .toBe('sábado 28, abril')
  expect(origin.format(format))
    .toBe('Saturday 28, April')
})

it('User custom locale', () => {
  expect(dayjs('2018-4-28')
    .locale('xx', {
      weekdays: Array(7).fill('week'),
      months: Array(12).fill('month')
    })
    .format(format))
    .toBe('week 28, month')
})

describe('Instance locale inheritance', () => {
  const esDayjs = dayjs('2018-4-28').locale(es)

  it('Clone', () => {
    expect(esDayjs.clone().format(format))
      .toBe('sábado 28, abril')
    expect(dayjs(esDayjs).format(format))
      .toBe('sábado 28, abril')
  })

  it('StartOf EndOf', () => {
    expect(esDayjs.startOf('year').format(format))
      .toBe('lunes 1, enero')
    expect(esDayjs.endOf('day').format(format))
      .toBe('sábado 28, abril')
  })

  it('Set', () => {
    expect(esDayjs.set('year', 2017).format(format))
      .toBe('viernes 28, abril')
  })

  it('Add', () => {
    expect(esDayjs.add(1, 'year').format(format))
      .toBe('domingo 28, abril')
    expect(esDayjs.add(1, 'month').format(format))
      .toBe('lunes 28, mayo')
    expect(esDayjs.add(1, 'minute').format(format))
      .toBe('sábado 28, abril')
  })

  it('dayjs.locale() returns locale name', () => {
    dayjs.locale(es)
    moment.locale('es')
    expect(dayjs.locale()).toBe(moment.locale())

    dayjs.locale('en')
    moment.locale('en')
    expect(dayjs.locale()).toBe(moment.locale())
  })
})


it('Not supported locale string fallback to previous one (instance)', () => {
  const D = dayjs()
  expect(D.locale()).toBe('en')
  const D2 = D.locale(NOT_SUPPORTED_LOCALE_STRING)
  expect(D2.locale()).toBe('en')
  expect(D2.format()).toBe(D.format())
  const D3 = D2.locale('es')
  expect(D3.locale()).toBe('es')
  const D4 = D3.locale(NOT_SUPPORTED_LOCALE_STRING)
  expect(D4.locale()).toBe('es')
})

it('Not supported locale string fallback to previous one (global)', () => {
  expect(dayjs().locale()).toBe('en')
  dayjs.locale(NOT_SUPPORTED_LOCALE_STRING)
  expect(dayjs().locale()).toBe('en')
  dayjs.locale('es')
  expect(dayjs().locale()).toBe('es')
  dayjs.locale(NOT_SUPPORTED_LOCALE_STRING)
  expect(dayjs().locale()).toBe('es')
})