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Testing Negative Year Date Handling in Day.js

This test suite validates the negativeYear plugin functionality in Day.js, focusing on parsing, manipulating, and comparing dates with negative years. The tests ensure robust handling of dates before year 0, including integration with other plugins and various date format scenarios.

Test Coverage Overview

The test suite provides comprehensive coverage of negative year date handling capabilities:

Parsing negative year dates in different formats
Validation of non-negative year handling
Integration with UTC plugin
Date arithmetic with negative years
Date comparison operations

Implementation Analysis

The testing approach utilizes Jest’s describe/it pattern for organized test grouping. MockDate is employed for consistent date handling during tests. The implementation validates both standard operations and edge cases, ensuring the plugin maintains compatibility with Day.js’s core functionality.

Tests verify format parsing, arithmetic operations, and comparison methods specifically for negative year scenarios.

Technical Details

Testing tools and setup:

Jest as the testing framework
MockDate for date mocking
Day.js plugin extension system
REGEX_PARSE constant for format validation
UTC plugin for timezone handling

Best Practices Demonstrated

The test suite exemplifies several testing best practices:

Proper test isolation using beforeEach/afterEach hooks
Comprehensive edge case coverage
Clear test case organization
Plugin interaction testing
Consistent assertion patterns

iamkun/dayjs

test/plugin/negativeYear.test.js

            
import MockDate from 'mockdate'
import dayjs from 'dayjs'
import negativeYear from '../../src/plugin/negativeYear'
import utc from '../../src/plugin/utc'
import { REGEX_PARSE } from '../../src/constant'


dayjs.extend(negativeYear)
dayjs.extend(utc)

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

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

describe('negativeYear', () => {
  it('parses negative years', () => {
    expect(dayjs('-2020-01-01').year()).toBe(-2020)
    const date = '-2021/01/03'
    const date2 = '01/03/-2021'
    const date3 = '01-03--2021'
    const d = date.match(REGEX_PARSE)
    expect(dayjs(date).format('YYYY-MM-DD')).toBe('-2021-01-03')
    expect(dayjs(date2).format('YYYY-MM-DD')).toBe('Invalid Date')
    expect(dayjs(date3).format()).toBe('Invalid Date')
    expect(d).toBe(null)
  })

  it('does not parse non-negative years', () => {
    expect(dayjs('2020-01-01').year()).toBe(2020)
  })

  it('works with other plugins', () => {
    expect(dayjs.utc('-2020-01-01').year()).toBe(-2020)
  })

  it('Add and subtract with negative years', () => {
    expect(dayjs('-2006').add(1, 'y')).toEqual(dayjs('-2005'))
    expect(dayjs('-2006').subtract(1, 'y')).toEqual(dayjs('-2007'))
    expect(dayjs('-2006').add(1, 'y').format('YYYY')).toBe(dayjs('-2005').format('YYYY'))
    expect(dayjs('-2006').subtract(1, 'y').format('YYYY')).toBe(dayjs('-2007').format('YYYY'))
  })

  it('Compare date with negative years', () => {
    expect(dayjs('-2006').isAfter(dayjs('-2007'))).toBeTruthy()
    expect(dayjs('-2006').isBefore(dayjs('-2005'))).toBeTruthy()
    expect(dayjs('-2006').isSame('-2006')).toBeTruthy()
  })
})