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Validating Constructor Type Checking in Day.js

This test suite validates core constructor functionality and type checking in Day.js, focusing on instance verification and object type detection. The tests ensure proper instance creation and reliable object type validation across different Day.js versions.

Test Coverage Overview

The test suite provides comprehensive coverage of Day.js constructor and type checking mechanisms.

Key areas tested include:

Instance type verification using instanceof operator
Cross-version object validation using $isDayjsObject property
Object type discrimination between Day.js instances and native Date objects

Implementation Analysis

The testing approach utilizes Jest’s describe/it pattern with MockDate for consistent date handling. Tests employ type checking patterns specific to JavaScript class instances and object properties.

Implementation features:

MockDate setup and teardown in beforeEach/afterEach hooks
Boolean assertions using toBeTruthy/toBeFalsy
Mock object creation for version compatibility testing

Technical Details

Testing infrastructure includes:

Jest as the primary testing framework
MockDate library for date manipulation
ES6 import syntax for module loading
Beforeach/afterEach hooks for test isolation

Best Practices Demonstrated

The test suite exemplifies several testing best practices for JavaScript libraries.

Notable practices include:

Proper test isolation through MockDate setup/teardown
Clear test case naming conventions
Comprehensive type checking scenarios
Efficient test organization with focused, single-purpose test cases

iamkun/dayjs

test/constructor.test.js

            
import MockDate from 'mockdate'
import dayjs from '../src'

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

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

it('supports instanceof dayjs', () => {
  expect(dayjs() instanceof dayjs).toBeTruthy()
})

it('$isDayjsObject', () => {
  const mockOtherVersionDayjsObj = {
    $isDayjsObject: true
  }
  expect(dayjs.isDayjs(mockOtherVersionDayjsObj)).toBeTruthy()
})

it('does not break isDayjs', () => {
  expect(dayjs.isDayjs(dayjs())).toBeTruthy()
  expect(dayjs.isDayjs(new Date())).toBeFalsy()
})