Testing

ts-datetime is rigorously tested to ensure reliability and correctness. This page outlines the testing approach and provides guidance for testing your own code that uses the library.

Library Test Coverage

The ts-datetime library itself is tested using a comprehensive test suite that covers:

• Core functionality
• Edge cases
• Localization
• Configuration variants
• Performance benchmarks

All public API methods are tested with a variety of inputs and expected outputs.

Testing Your Code

Mocking Current Time

When testing code that uses ts-datetime, you might need to mock the current time. Here's how:

import { Datetime } from 'ts-datetime'

// Save the original now method
const originalNow = Date.now

// Mock current time to a specific timestamp
Date.now = jest.fn(() => new Date('2024-01-01T12:00:00Z').getTime())

// Your test code
test('feature works with fixed time', () => {
  const now = Datetime.now()
  expect(now.year).toBe(2024)
  expect(now.month).toBe(1)
  expect(now.day).toBe(1)
})

// Restore original after tests
afterAll(() => {
  Date.now = originalNow
})

Test Helpers

You can create test helpers to simplify datetime testing:

// dateHelpers.ts
export function createFixedDatetime(dateString: string) {
  return new Datetime(dateString)
}

export function expectDateEqual(date: Datetime, year: number, month: number, day: number) {
  expect(date.year).toBe(year)
  expect(date.month).toBe(month)
  expect(date.day).toBe(day)
}

Testing Format Output

When testing formatted outputs, be explicit about the format to avoid test fragility:

test('formatting works correctly', () => {
  const date = new Datetime('2024-01-15T14:30:45Z')

  // ✅ Good - explicitly specify format
  expect(date.format('YYYY-MM-DD')).toBe('2024-01-15')

  // ❌ Fragile - depends on default format which could change
  expect(date.toString()).toBe('2024-01-15T14:30:45Z')
})

Testing Date Comparisons

When testing date comparisons, ensure proper timezone handling:

test('date comparisons work correctly', () => {
  const date1 = new Datetime('2024-01-01T00:00:00Z')
  const date2 = new Datetime('2024-01-02T00:00:00Z')

  expect(date1.isBefore(date2)).toBe(true)
  expect(date2.isAfter(date1)).toBe(true)
  expect(date1.isSame(date1.clone())).toBe(true)
})

Test Strategies

Unit Testing

For unit testing components that use ts-datetime:

test('DateDisplay component shows formatted date', () => {
  const fixedDate = new Datetime('2024-01-15')
  const component = render(<DateDisplay date={fixedDate} />)
  expect(component.getByText('January 15, 2024')).toBeInTheDocument()
})

Integration Testing

For integration testing with time-dependent features:

test('Scheduled notifications are sent at the right time', async () => {
  // Mock time
  jest.useFakeTimers()
  Date.now = jest.fn(() => new Date('2024-01-01T11:59:50Z').getTime())

  // Set up a notification for noon
  const scheduler = new Scheduler()
  scheduler.scheduleFor(Datetime.fromString('12:00'))

  // Fast-forward time
  jest.advanceTimersByTime(15 * 1000) // 15 seconds

  // Check notification was sent
  expect(notificationSpy).toHaveBeenCalled()
})

Common Test Pitfalls

• Timezone differences: Be explicit about timezones in tests to avoid inconsistencies
• DST transitions: Be aware of daylight saving time transitions in tests that span these periods
• Date equality: Use isSame() rather than object equality checks
• Format dependencies: Don't rely on default formatting in tests