You want to use jest to write tests that assert how dates compare to eachother. As part of that goal, you want to avoid all the repetitive patterns that arise in doing so and you want to get valueable feedback when tests fail.
The jest-date library provides a set of custom jest matchers
that you can use to extend jest. These will make your tests more declarative,
clear to read and to maintain. Next to that, it will give you valueable information as to why your test are failing.
This module is distributed via npm which is bundled with node and
should be installed as one of your project's devDependencies:
npm install --save-dev jest-date
Import jest-date once (for instance in your tests setup
file) and you're good to go:
import 'jest-date'Note: If you're using TypeScript, make sure your setup file is a
.tsand not a.jsto include the necessary types.
Alternatively, you can selectively import only the matchers you intend to use,
and extend jest's expect yourself:
import {
toBeBefore,
toBeSameMonthAs,
} from 'jest-date/matchers'
expect.extend({toBeBefore, toBeSameMonthAs})Note: when using TypeScript, this way of importing matchers won't provide the necessary type definitions.
Relative matchers can be used to compare two dates with eachother. When a matcher fails, it will provide a debug message in the following format:
Expected date {expected_date} {matcher} {received_date}, but it was {difference}.
Here are some concrete examples:
toBeSameSecondAs:
Expected date 2020-07-13T22:05:23.670Z to be same second as 2020-07-13T22:05:22.670Z, but it was 1 second after.
toBeBefore:
Expected date 1970-01-01T00:00:00.000Z not to be before 2020-01-01T00:00:00.000Z, but it was 50 years before.
toBeSameQuarterAs:
Expected date 2020-10-13T22:15:12.304Z to be same quarter as 2020-07-13T22:15:12.304Z, but it was 3 months after.
Weekday matchers can be used to check if a given date falls on a certain day of the week. When this kind of a matcher fails, it will provide a debug message in either the following formats:
Standard Message: Expected date {received} to be on a {expected_day}, but it was on a {actual_day}.
Inverted Message: Expected date {received} not be on a {expected_day}, but it was
Here are some concrete examples:
toBeMonday:
Expected date 2020-07-13T22:25:43.553Z to be on a monday, but it was on a tuesday.
toBeSunday:
Expected date 2020-07-11T22:26:33.626Z not to be on a sunday, but it was.
jest-date can work with any library or framework. The custom matcher examples below are written using
functions from the awesome date-fns library (e.g. isBefore,
isSameDayAs, formatDistance, etc.)
Matcher type: relative
toBeBefore(date: Date)This allows you to check whether a date is before another.
expect(new Date('1970')).toBeBefore(new Date('2020')) // ✔️ pass
expect(new Date('2020')).toBeBefore(new Date('1970')) // ❌ fail
expect(new Date('1970')).not.toBeBefore(new Date('2020')) // ❌ fail
expect(new Date('2020')).not.toBeBefore(new Date('1970')) // ✔️ passMatcher type: relative
toBeAfter(date: Date)This allows you to check whether a date is after another.
expect(new Date('2020')).toBeAfter(new Date('1970')) // ✔️ pass
expect(new Date('1970')).toBeAfter(new Date('2020')) // ❌ fail
expect(new Date('2020')).not.toBeAfter(new Date('1970')) // ❌ fail
expect(new Date('1970')).not.toBeAfter(new Date('2020')) // ✔️ passMatcher type: relative
toBeSameSecondAs(date: Date)This allows you to check whether a date is in the same second as another.
import {startOfSecond, addSeconds} from 'date-fns'
const date = new Date()
expect(startOfSecond(date)).toBeSameSecondAs(date) // ✔️ pass
expect(addSeconds(date, 2)).toBeSameSecondAs(date) // ❌ fail
expect(startOfSecond(date)).not.toBeSameSecondAs(date) // ❌ fail
expect(addSeconds(date, 2)).not.toBeSameSecondAs(date) // ✔️ passMatcher type: relative
toBeSameMinuteAs(date: Date)This allows you to check whether a date is in the same minute as another.
import {startOfMinute, addMinutes} from 'date-fns'
const date = new Date()
expect(startOfMinute(date)).toBeSameMinuteAs(date) // ✔️ pass
expect(addMinutes(date, 2)).toBeSameMinuteAs(date) // ❌ fail
expect(startOfMinute(date)).not.toBeSameMinuteAs(date) // ❌ fail
expect(addMinutes(date, 2)).not.toBeSameMinuteAs(date) // ✔️ passMatcher type: relative
toBeSameHourAs(date: Date)This allows you to check whether a date is in the same hour as another.
import {startOfHour, addHours} from 'date-fns'
const date = new Date()
expect(startOfHour(date)).toBeSameHourAs(date) // ✔️ pass
expect(addHours(date, 2)).toBeSameHourAs(date) // ❌ fail
expect(startOfHour(date)).not.toBeSameHourAs(date) // ❌ fail
expect(addHours(date, 2)).not.toBeSameHourAs(date) // ✔️ passMatcher type: relative
toBeSameDayAs(date: Date)This allows you to check whether a date is in the same day as another.
import {startOfDay, addDays} from 'date-fns'
const date = new Date()
expect(startOfDay(date)).toBeSameDayAs(date) // ✔️ pass
expect(addDays(date, 2)).toBeSameDayAs(date) // ❌ fail
expect(startOfDay(date)).not.toBeSameDayAs(date) // ❌ fail
expect(addDays(date, 2)).not.toBeSameDayAs(date) // ✔️ passMatcher type: relative
toBeSameWeekAs(date: Date)This allows you to check whether a date is in the same week as another.
import {startOfWeek, addWeeks} from 'date-fns'
const date = new Date()
expect(startOfWeek(date)).toBeSameWeekAs(date) // ✔️ pass
expect(addWeeks(date, 2)).toBeSameWeekAs(date) // ❌ fail
expect(startOfWeek(date)).not.toBeSameWeekAs(date) // ❌ fail
expect(addWeeks(date, 2)).not.toBeSameWeekAs(date) // ✔️ passMatcher type: relative
toBeSameMonthAs(date: Date)This allows you to check whether a date is in the same month as another.
import {startOfMonth, addMonths} from 'date-fns'
const date = new Date()
expect(startOfMonth(date)).toBeSameMonthAs(date) // ✔️ pass
expect(addMonths(date, 2)).toBeSameMonthAs(date) // ❌ fail
expect(startOfMonth(date)).not.toBeSameMonthAs(date) // ❌ fail
expect(addMonths(date, 2)).not.toBeSameMonthAs(date) // ✔️ passMatcher type: relative
toBeSameQuarterAs(date: Date)This allows you to check whether a date is in the same quarter as another.
import {startOfQuarter, addQuarters} from 'date-fns'
const date = new Date()
expect(startOfQuarter(date)).toBeSameQuarterAs(date) // ✔️ pass
expect(addQuarters(date, 2)).toBeSameQuarterAs(date) // ❌ fail
expect(startOfQuarter(date)).not.toBeSameQuarterAs(date) // ❌ fail
expect(addQuarters(date, 2)).not.toBeSameQuarterAs(date) // ✔️ passMatcher type: relative
toBeSameYearAs(date: Date)This allows you to check whether a date is in the same year as another.
import {startOfYear, addYears} from 'date-fns'
const date = new Date()
expect(startOfYear(date)).toBeSameYearAs(date) // ✔️ pass
expect(addYears(date, 2)).toBeSameYearAs(date) // ❌ fail
expect(startOfYear(date)).not.toBeSameYearAs(date) // ❌ fail
expect(addYears(date, 2)).not.toBeSameYearAs(date) // ✔️ passMatcher type: weekday
toBeMonday()This allows you to check whether a date is on a monday.
expect(new Date()).toBeMonday()
expect(new Date()).not.toBeMonday()Matcher type: weekday
toBeTuesday()This allows you to check whether a date is on a tuesday.
expect(new Date()).toBeTuesday()
expect(new Date()).not.toBeTuesday()Matcher type: weekday
toBeWednesday()This allows you to check whether a date is on a wednesday.
expect(new Date()).toBeWednesday()
expect(new Date()).not.toBeWednesday()Matcher type: weekday
toBeThursday()This allows you to check whether a date is on a thursday.
expect(new Date()).toBeThursday()
expect(new Date()).not.toBeThursday()Matcher type: weekday
toBeFriday()This allows you to check whether a date is on a friday.
expect(new Date()).toBeFriday()
expect(new Date()).not.toBeFriday()Matcher type: weekday
toBeSaturday()This allows you to check whether a date is on a saturday.
expect(new Date()).toBeSaturday()
expect(new Date()).not.toBeSaturday()Matcher type: weekday
toBeSunday()This allows you to check whether a date is on a Sunday.
expect(new Date()).toBeSunday()
expect(new Date()).not.toBeSunday()This library was created because as far as I know, there is no matcher library out there dedicated to only comparing dates. I ended up using the functions from date-fns to create assertions like this one:
expect(isSameDay(date1, date2)).toBe(true)But when this fails, you get no feedback at all other than the fact that the dates are not the same day. By making date matchers with helpful failure messages, I hope to make the debugging lives of developers a little bit easier.
Project structure and tooling hugely inspired by @testing-library/jest-dom
MIT