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Testing English Locale Date Formatting in dayjs

This test suite validates Day.js date formatting functionality across multiple English locale variants. It ensures consistent date format handling for en, en-gb, en-in, and en-tt locales while testing the localizedFormat plugin integration.

Test Coverage Overview

The test suite provides comprehensive coverage of Day.js locale-specific date formatting.

Key areas tested include:

Standard English (en) date format validation
British (en-gb) date format verification
Indian (en-in) locale format testing
Trinidad and Tobago (en-tt) date patterns
Integration with localizedFormat plugin

Implementation Analysis

The testing approach utilizes Jest’s describe/it pattern with dynamic test generation through array iteration. It implements parameterized testing to validate multiple locale configurations efficiently.

Technical implementation features:

Dynamic test generation using forEach loop
Locale-specific date format validation
Plugin extension verification
Template literal usage for test descriptions

Technical Details

Testing infrastructure includes:

Jest testing framework
Day.js library and locale modules
LocalizedFormat plugin integration
Test configuration using locale objects
Format pattern ‘L’ for localized date testing

Best Practices Demonstrated

The test suite exemplifies several testing best practices for date handling and internationalization.

Notable practices include:

Parameterized testing for multiple locales
Consistent test structure and naming
Isolated locale testing
Clear expected vs actual value comparisons
Modular test organization

iamkun/dayjs

test/locale/en.test.js

            
import dayjs from '../../src'
import '../../src/locale/en'
import '../../src/locale/en-gb'
import '../../src/locale/en-in'
import '../../src/locale/en-tt'
import localizedFormat from '../../src/plugin/localizedFormat'

dayjs.extend(localizedFormat)

const locales = [
  { locale: 'en', expectedDate: '12/25/2019' },
  { locale: 'en-gb', expectedDate: '25/12/2019' },
  { locale: 'en-in', expectedDate: '25/12/2019' },
  { locale: 'en-tt', expectedDate: '25/12/2019' }
]

describe('English date formats', () => {
  locales.forEach((locale) => {
    it(`should correctly format date with locale - ${locale.locale}`, () => {
      const dayjsWithLocale = dayjs('2019-12-25').locale(locale.locale)
      expect(dayjsWithLocale.format('L')).toEqual(locale.expectedDate)
    })
  })
})