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Serenity/JS is an innovative open-source framework designed to make acceptance and regression testing of complex software systems faster, more collaborative and easier to scale.

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Serenity/JS Assertions

@serenity-js/assertions is an assertions library implementing the Screenplay Pattern.


To install this module, run the following command in your computer terminal:

npm install --save-dev @serenity-js/core @serenity-js/assertions

To learn more about Serenity/JS and how to use it on your project, follow the Serenity/JS Getting Started guide.

Performing verifications using Ensure

import { Ensure, endsWith } from '@serenity-js/assertions'
import { actorCalled } from '@serenity-js/core'
import { Navigate, Page } from '@serenity-js/web'

await actorCalled('Erica').attemptsTo(''),

Controlling execution flow using Check

import { actorCalled } from '@serenity-js/core'
import { Check } from '@serenity-js/assertions'
import { Click, isVisible } from '@serenity-js/protractor'

await actorCalled('Erica').attemptsTo(
Check.whether(NewsletterModal, isVisible())

Synchronising the test with the System Under Test using Wait

import { actorCalled } from '@serenity-js/core'
import { Click, isVisible, Wait } from '@serenity-js/protractor'

await actorCalled('Erica').attemptsTo(
Wait.until(CloseModalButton, isVisible()),

Defining custom expectations using Expectation.thatActualShould

import { actorCalled } from '@serenity-js/core'
import { Expectation, Ensure } from '@serenity-js/assertions'

function isDivisibleBy(expected: Answerable<number>): Expectation<number> {
return Expectation.thatActualShould<number, number>('have value divisible by', expected)
.soThat((actualValue, expectedValue) => actualValue % expectedValue === 0)

await actorCalled('Erica').attemptsTo(
Ensure.that(4, isDivisibleBy(2)),

Composing expectations using

import { actorCalled } from '@serenity-js/core'
import { Expectation, Ensure, and, or, isGreaterThan, isLessThan, equals } from '@serenity-js/assertions'

function isWithin(lowerBound: number, upperBound: number) {
return Expectation
.to(`have value within ${ lowerBound } and ${ upperBound }`)
or(isGreaterThan(lowerBound), equals(lowerBound)),
or(isLessThan(upperBound), equals(upperBound)),

await actorCalled('Erica').attemptsTo(
Ensure.that(5, isWithin(3, 6)),

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