Send and receive email in Cypress JS tests with MailSlurp

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Test email sign-up, password verification and more with Cypress JS and MailSlurp. Capture OTP magic links and test auth flows end-to-end.

test email with cypress js
Send and receive emails in Cypress JS to test application sign-up, verification and notifications.

Cypress JS is a powerful web testing framework that allows automated tests using real browsers. With MailSlurp you can test using real email accounts created on demand - for free.

In this example we will see how to test login and sign up using one-time disposable email addresses and a real web app.

Integration options

You can use email with Cypress in two ways: using the mailslurp-client package that gives full access to the API OR using the official MailSlurp Cypress Plugin with Cypress convenience methods. This guide covers usage of Cypress with the mailslurp-client npm package. Use the cypress-mailslurp plugin instead if you want the cy.mailslurp() extensions available in your project.

Cypress JS

Cypress is an amazing end-to-end testing framework. It's popular, bundles its own chrome browser and is easily extended. Cypress lets you test many parts of a website or web application with a browser in an automated way. It's like Selenium but a lot more user-friendly.

Testing with real email addresses

Many application use emails for account login and creation. Testing logins with Cypress is easy if you have a designated test user - but what about sign ups?

Email sign up has to be the most important aspect of any application and without access to unique, private email addresses end-to-end testing is difficult.

Luckily there's MailSlurp, a free API that lets you create real, randomized email addresses on demand. It also lets you send and receive email programmatically - perfect for end-to-end testing user sign-up flows!

An example

To demonstrate Cypress testing we'll use the MailSlurp Authentication Playground app. It's a dummy React application that has a user sign-up process. To test this process end-to-end we will:

  • Load the playground in Cypress
  • Create a test email address with MailSlurp
  • Sign up for using the email address
  • Receiving a confirmation email
  • Extract the confirmation code and confirm the user

Setup Cypress

To setup make sure you have NodeJS installed then run:

npm install --save cypress mailslurp

Your package.json should look something like this:

  "description": "Example of using emails with Cypress JS",
  "scripts": {
    "test": "cypress run",
    "dev": "cypress open",
    "postinstall": "cypress install"
  "dependencies": {
    "cypress": "^10.5.0",
    "mailslurp-client": "^15.13.3"

Next we need to create a cypress.config.js file. We will set defaultCommandTimeout and requestTimeout to 30 seconds so that our tests have time to wait for emails to be sent or received. We'll also add some viewport dimensions to the Cypress browser.

const { defineConfig } = require('cypress')

module.exports = defineConfig({
  defaultCommandTimeout: 30000,
  requestTimeout: 30000,
  viewportHeight: 800,
  viewportWidth: 800,
  videoCompression: false,
  e2e: {
    setupNodeEvents(on, config) {},

Setup MailSlurp

In order to use MailSlurp with Cypress we will define some custom commands.

To avoid creating custom commands check out the MailSlurp Cypress Plugin instead.

To do that create a cypress/support directory and add e2e.js and commands.js if not already present.

└── support
    └── commands.js
    └── e2e.js

Inside e2e.js import the commands file.

import './commands'

Now inside commands let's import and configure a MailSlurp client - this will let us send and receive emails. Make sure you have a free MailSlurp API Key first.

const { MailSlurp } = require('mailslurp-client');
// set your api key with an environment variable `CYPRESS_API_KEY` or configure using `env` property in config file
// (cypress prefixes environment variables with CYPRESS)
const apiKey = Cypress.env('API_KEY')
const mailslurp = new MailSlurp({ apiKey });

Cypress.Commands.add("createInbox", () => {
  return mailslurp.createInbox();

Cypress.Commands.add("waitForLatestEmail", (inboxId) => {
  // how long we should hold connection waiting for an email to arrive
  const timeoutMillis = 30_000;
  return mailslurp.waitForLatestEmail(inboxId, timeoutMillis)

Set API Key environment variable

The MailSlurp config we created requires an API KEY to be set with the CYPRESS_API_KEY environment variable.

On Linux/Mac run cypress commands like so:

CYPRESS_API_KEY=your-api-key cypress run

For Windows environments run:

cypress run;

Calling custom commands

Now in Cypress tests we can do the following:

cy.createInbox().then((inbox) => {
  // { id: '...', emailAddress: '...' }


cy.waitForLatestEmail( => {
  // { subject: '...', body: '...' }

You can also add your own custom commands for any functions you want to call on the MailSlurp email API.

Create test structure

So in order to test a sign-up flow end-to-end we need an integration test. Create a test spec in the cypress/integration folder structure:

touch cypress/e2e/

The test should be located as follows:

└── e2e
    └── example.spec.js

Inside e2e/ let's write our first test.

Writing a test

Let's start simple and write a test to load the MailSlurp playground app in Cypress.

That would look a little like this:

it('can load oauth demo site', () => {
  cy.contains('Sign in to your account');

Next we want to click a sign up button to begin the sign up process.

it('can click sign up link', () => {
  cy.contains('Testable Sign Up Form');

Running tests

To run the test run CYPRESS_API_KEY=your-api-key npx cypress run.

Cypress will open:

cypress test email
Open Cypress and run tests

Click the spec runs our test. Our clicked Cypress loads the Playground app and asserts that a sign-in message is displayed on the page, it then clicks the sign-up link.

The output looks like this:

cypress playground
cypress disposable email

Testing with emails in Cypress

Now let's integrate email address into our test using MailSlurp. MailSlurp requires an api key but it's free for personal use so sign up to get one.

Once you've sign up we can extend Cypress with a command to creates new email address when we need them.

Using our createInbox command

Now that we have a Cypress command that returns a new email address we can put it all together in our sign up test. Inside the same describe method add the following:

const password = "test-password";
let inboxId;
let emailAddress;
it('can generate a new email address and sign up', () => {
  // see commands.js custom commands
  cy.createInbox().then(inbox => {
    // verify a new inbox was created

    // save the inboxId for later checking the emails
    inboxId =
    emailAddress = inbox.emailAddress;

    // sign up with inbox email address and the password

Now we can run our tests again

npx cypress run

Cypress loads our login screen and enters a real address that was generated with MailSlurp. We then see a confirm screen:

cypressjs email codes

Receive confirmation email

Once we have submitted our new user sign-up the Playground will send a confirmation email with a code that we need to enter. We can receive this email using MailSlurp:

let code;
it('can receive the confirmation email and extract the code', () => {
  // wait for an email in the inbox
  cy.waitForLatestEmail(inboxId).then(email => {
    // verify we received an email

    // verify that email contains the code
    assert.strictEqual(/verification code is/.test(email.body), true);

    // extract the confirmation code (so we can confirm the user)
    code = /([0-9]{6})$/.exec(email.body)[1];

Running the tests shows that Cypress waits for and extracts the email content:

read emails cypress

Confirm the user

Finally we can use the extracted email code to confirm the user:

it('can enter confirmation code and confirm user', () => {

Now we can use Cypress to login with our confirmed email address and password:

it('can log in with confirmed account', () => {
  cy.contains('Sign in to your account');
  // fill out username (email) and password
  // submit
submit form cypressjs

If successful the Playground will show a picture of a happy dog. Let's test for that:

it('shows the successful greeting', () => {
happy dog
Application showing welcome dog when login succeeds.

Next Steps

Testing with real emails means truly testing your app's most important processes like user sign up and email verification. MailSlurp makes Cypress email testing easy!

For more information on receiving emails in tests see the developers sections.

Code Samples

As always you can find this and other examples in the MailSlurp examples repository. Use MailSlurp free and take your end-to-end test coverage to 💯 !