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Testing Locale Data Plugin Implementation in Day.js

This test suite validates the localeData plugin functionality in Day.js, ensuring proper localization features across different languages and date formats. The tests compare Day.js implementation against Moment.js to verify consistent behavior in handling various locale-specific date operations.

Test Coverage Overview

The test suite provides comprehensive coverage of locale-specific date operations:

Tests multiple locales including zh-cn, en, fr, and ru
Validates month and weekday formatting across locales
Verifies long date format patterns
Tests both instance and global localeData methods
Covers meridiem and ordinal functions

Implementation Analysis

The testing approach uses Jest’s describe/it pattern for structured test organization. Each test case implements direct comparisons between Day.js and Moment.js outputs to ensure compatibility. The suite employs MockDate for consistent date handling across test runs.

Key patterns include locale switching, format verification, and array equality checks using Jest’s expect assertions.

Technical Details

Testing infrastructure includes:

Jest as the primary testing framework
MockDate for date manipulation
Multiple locale imports (fr, ru, zh-cn)
Plugin extensions: localeData and localizedFormat
Moment.js as reference implementation

Best Practices Demonstrated

The test suite exemplifies several testing best practices:

Consistent setup/teardown using beforeEach/afterEach hooks
Systematic locale testing across multiple languages
Comprehensive format verification
Modular test organization
Clear test case isolation
Thorough edge case handling

iamkun/dayjs

test/plugin/localeData.test.js

            
import MockDate from 'mockdate'
import moment from 'moment'
import dayjs from '../../src'
import '../../src/locale/fr'
import '../../src/locale/ru'
import '../../src/locale/zh-cn'
import localeData from '../../src/plugin/localeData'
import localizedFormat from '../../src/plugin/localizedFormat'

dayjs.extend(localizedFormat)
dayjs.extend(localeData)

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

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

describe('Instance localeData', () => {
  ['zh-cn', 'en', 'fr'].forEach((lo) => {
    it(`Locale: ${lo}`, () => {
      dayjs.locale(lo)
      moment.locale(lo)
      const d = dayjs()
      const m = moment()
      const dayjsLocaleData = dayjs().localeData()
      const momentLocaleData = moment().localeData()
      expect(dayjsLocaleData.firstDayOfWeek()).toBe(momentLocaleData.firstDayOfWeek())
      expect(dayjsLocaleData.months(d)).toBe(momentLocaleData.months(m))
      expect(dayjsLocaleData.months()).toEqual(momentLocaleData.months())
      expect(dayjsLocaleData.monthsShort(d)).toBe(momentLocaleData.monthsShort(m))
      expect(dayjsLocaleData.monthsShort()).toEqual(momentLocaleData.monthsShort())
      expect(dayjsLocaleData.weekdays(d)).toBe(momentLocaleData.weekdays(m))
      expect(dayjsLocaleData.weekdays()).toEqual(momentLocaleData.weekdays())
      expect(dayjsLocaleData.weekdaysMin(d)).toBe(momentLocaleData.weekdaysMin(m))
      expect(dayjsLocaleData.weekdaysMin()).toEqual(momentLocaleData.weekdaysMin())
      expect(dayjsLocaleData.weekdaysShort(d)).toBe(momentLocaleData.weekdaysShort(m))
      expect(dayjsLocaleData.weekdaysShort()).toEqual(momentLocaleData.weekdaysShort())
      const longDateFormats = ['LT', 'LTS', 'L', 'LL', 'LLL', 'LLLL', 'l', 'll', 'lll', 'llll']
      longDateFormats.forEach((f) => {
        expect(dayjsLocaleData.longDateFormat(f)).toEqual(momentLocaleData.longDateFormat(f))
      })
    })
  })
  dayjs.locale('en')
  moment.locale('en')
})


it('Global localeData', () => {
  ['zh-cn', 'en', 'fr'].forEach((lo) => {
    dayjs.locale(lo)
    moment.locale(lo)
    const dayjsLocaleData = dayjs.localeData()
    const momentLocaleData = moment.localeData()
    expect(dayjsLocaleData.firstDayOfWeek()).toBe(momentLocaleData.firstDayOfWeek())
    expect(dayjsLocaleData.months()).toEqual(momentLocaleData.months())
    expect(dayjsLocaleData.monthsShort()).toEqual(momentLocaleData.monthsShort())
    expect(dayjsLocaleData.weekdays()).toEqual(momentLocaleData.weekdays())
    expect(dayjsLocaleData.weekdaysShort()).toEqual(momentLocaleData.weekdaysShort())
    expect(dayjsLocaleData.weekdaysMin()).toEqual(momentLocaleData.weekdaysMin())
    const longDateFormats = ['LT', 'LTS', 'L', 'LL', 'LLL', 'LLLL', 'l', 'll', 'lll', 'llll']
    longDateFormats.forEach((f) => {
      expect(dayjsLocaleData.longDateFormat(f)).toEqual(momentLocaleData.longDateFormat(f))
    })
  })
})


it('Listing the months and weekdays', () => {
  ['zh-cn', 'en', 'fr'].forEach((lo) => {
    dayjs.locale(lo)
    moment.locale(lo)
    expect(dayjs.months()).toEqual(moment.months())
    expect(dayjs.monthsShort()).toEqual(moment.monthsShort())
    expect(dayjs.weekdays()).toEqual(moment.weekdays())
    expect(dayjs.weekdaysShort()).toEqual(moment.weekdaysShort())
    expect(dayjs.weekdaysMin()).toEqual(moment.weekdaysMin())
  })
})

it('Month function', () => {
  const dayjsLocaleData = dayjs().locale('ru').localeData()
  const momentLocaleData = moment().locale('ru').localeData()
  expect(dayjsLocaleData.months()).toEqual(momentLocaleData.months())
  expect(dayjsLocaleData.monthsShort()).toEqual(momentLocaleData.monthsShort())
  dayjs.locale('ru')
  moment.locale('ru')
  expect(dayjs.months()).toEqual(moment.months())
  expect(dayjs.monthsShort()).toEqual(moment.monthsShort())
})

it('Locale order', () => {
  dayjs.locale('fr')
  moment.locale('fr')
  expect(dayjs.weekdays(true)).toEqual(moment.weekdays(true))
  expect(dayjs.weekdaysShort(true)).toEqual(moment.weekdaysShort(true))
  expect(dayjs.weekdaysMin(true)).toEqual(moment.weekdaysMin(true))
  expect(dayjs.weekdays()).not.toEqual(dayjs.weekdays(true))
  dayjs.locale('en')
  moment.locale('en')
  expect(dayjs.weekdays(true)).toEqual(moment.weekdays(true))
})

it('meridiem', () => {
  dayjs.locale('zh-cn')
  expect(typeof dayjs.localeData().meridiem).toEqual('function')
  expect(typeof dayjs().localeData().meridiem).toEqual('function')
  dayjs.locale('en')
})

it('ordinal', () => {
  dayjs.locale('zh-cn')
  expect(typeof dayjs.localeData().ordinal).toEqual('function')
  expect(typeof dayjs().localeData().ordinal).toEqual('function')
  dayjs.locale('en')
})