Email Delivery Testing: Node.js, Cypress, and Mailsac

Email delivery testing is an essential part of ensuring your application sends emails correctly and efficiently. With Mailsac, you can take advantage of its powerful REST API to simplify your email testing process. In this blog post, we’ll show you how to use Cypress, a popular end-to-end testing framework, in combination with Mailsac for seamless email delivery testing. We’ll cover setting up the Cypress environment, running tests, and provide plenty of code samples to get you started.

Setting up the Cypress Environment

First, you’ll need to have Node.js installed on your computer. Once that’s done, follow these steps to set up Cypress:

1. Create a new directory for your project and navigate to it in the terminal. b. Run npm init to create a package.json file. c. Install Cypress by running npm install cypress. d. Add a script to your package.json file to run Cypress:

"scripts": {
  "cypress:open": "cypress open"

2. Configuring Cypress and Mailsac API

Next, create a cypress.json file in your project’s root directory. This file will store your Mailsac API key and other configuration options:

  "baseUrl": "",
  "env": {
    "mailsac_api_key": "your_mailsac_api_key"

Replace your_mailsac_api_key with your actual Mailsac API key.

3. Writing Your First Cypress Test

Now, let’s create a test file in the cypress/integration folder. Name it email_delivery_spec.js. In this file, we’ll write a test that sends an email to a random Mailsac address and then checks whether the email was received.

// cypress/integration/email_delivery_spec.js

describe("Email Delivery Test", () => {
  it("sends an email and verifies its receipt", async () => {
      const randomEmail = `test-${Math.random().toString(36).substring(2)}`;
      const testSubject = `Cypress Email Delivery Test ${Math.random().toString(36).substring(2)}`;
      const testBody = "This is a test email sent using Cypress and Mailsac.";

      // Send an email using your application's email sending method
      // ...
      // TOOD: integrate your app here!

      // Function to poll Mailsac API for received messages. It will be called
      // recursively.
      const checkEmail = async () => {
        let response = await cy.request({
          method: "GET",
          url: `${randomEmail}/messages`,
          headers: {
            // Get a mailsac api key at:
            "Mailsac-Key": Cypress.env("mailsac_api_key")
        const messages = response.body;
        const message = messages.find(msg => msg.subject === testSubject);

        if (!message) {
          return cy.wait(1000).then(() => {

        expect(message.from[0].address).to.equal("[email protected]");

        // Check email content for testBody text
        const textResponse = await cy.request(`${randomEmail}/${msg._id}`);

        // Clean up by deleting the received messages. This could also be done in an afterEach block.
        await Promise.all( =>
            method: "DELETE",
            url: `${randomEmail}/messages/${msg._id}`,
            headers: {
              "Mailsac-Key": Cypress.env("mailsac_api_key")

      // Start polling for received messages
      await checkEmail();

Replace [email protected] with your application’s sender email address.

This will open the Cypress Test Runner, and you’ll see your email_delivery_spec.js test listed. Click on the test to run it.

Running Selenium Tests in GitHub actions email test cover image

Run Selenium Tests in GitHub Actions – Email Testing

Welcome to the second part of the two-part series on running selenium tests with GitHub Actions. In the first article, we outlined how to get started and how to set up your repo for Actions. In this guide, we’ll outline how to run email integration tests and pass secrets to GitHub Actions.

To start… Why would you want to test emails with live email services in the first place? Can’t you simply write to a log file or standard out? Yes… and no. Writing to log files or standard out is ok at the beginning of the application lifecycle. Building out the email send feature takes a back seat to ensure the application actually works.

But let’s say your application is almost ready for its initial release. You want to test that you can even connect to an SMTP server. Or test to ensure the right message can go to the right inbox. Testing via log files or standard out starts to get a bit limiting in that regard. Additionally, say you want to be really sure that the contents of an email you send are what you expect them to be. At this point, you’d like to simulate as much of the email delivery as possible.

You can accomplish this with a disposable email service like Mailsac.

Allow us to plug our mail service

At Mailsac we focus on the developer experience around email automation and testing. That’s why we’ve made it so you can test out the API mentioned in this guide with a free account. You can sign up here.

So let’s lay out our testing goal:

  1. Simulate an email send with our sample application.
    1. Refer to our Guide To Stress Free Email Testing with Next.js for more information on how we created this sample application
    2. Use Selenium to drive the form and hit send
  2. Use our capture service API to send the email
  3. Use Mailsac’s API to read the email from the destination inbox
  4. Verify the contents of said email
  5. Do all this on GitHub Actions

Let’s get started.

API Credentials

If you don’t already have one, go ahead and create a mailsac account and generate an API key.

Plug those API keys in a file called .env at the root of the project:



Craft the Email

Let’s craft the email by driving Selenium through the form. Start by crafting a selenium test:

const chrome = require('selenium-webdriver/chrome');
const {Builder, Browser, By } = require('selenium-webdriver');

const screen = {
  width: 1920,
  height: 1080

(async function emailSendTest() {
  let driver = await new Builder()
    // .setChromeOptions(new chrome.Options().headless().windowSize(screen))

  try {
    await driver.get('<http://localhost:3000>');
    let didSendButtonRender = await driver.findElement('sendbutton')).isDisplayed()
    if (!didSendButtonRender){
      throw new Error(`Send button was not rendered properly.`);
    await driver.findElement('email')).sendKeys("[email protected]");
    await driver.findElement('comment')).sendKeys("This is some text from our Selenium test.");
    await driver.findElement('sendbutton')).click();

  } finally {
    await driver.quit();


Note: I left the headless option off for this first test. You’ll want to turn the headless option back on for the test run via our continuous integration environment.

You can do a local test by running

node tests/email-send.js

And checking the inbox we tested ([email protected]) manually:

Success! Though that’s part of the way there. Let’s assert that the email contents match via the API.

Read the Email via Mailsac’s API

Thankfully, Mailsac has not only a robust API but also lots of sample code inside the docs. We’ll lift the sample email read from here:

Note that you’ll need to install a couple of dev packages to get this to work: dotenv and superagent. dotenv is needed in this instance since our tests don’t load the entire next framework and as such, we need a method to read your .env file. superagent is a small client-side HTTP request library for doing quick HTTP calls like the one we’re about to do.

So go ahead and add them to your developer dependencies:

npm install --save-dev dotenv superagent

And add our own text comparison to Mailsac’s sample code:


const superagent = require('superagent')
const mailsac_api_key = process.env.MAILSAC_API_KEY
const expected_message = 'This is some text from our Selenium test.'

  .get('<[email protected]/messages>')
  .set('Mailsac-Key', mailsac_api_key)
  .then((messages) => {
      const messageId = messages.body[0]._id
          .get('<[email protected]/>' + messageId)
          .set('Mailsac-Key', mailsac_api_key)
              .then((messageText) => {
                  if (messageText.text !== expected_message)  {
                    throw new Error(`Message '${messageText.text}' does not match expected text '${expected_message}'`)
                    console.log("Message comparison passed");
  .catch(err => {


Running the test locally should result in a passing test:

$ node tests/email-read.js
Message comparison passed

Of course, if we’ll run these tests many times we’ll also want to ensure that we delete the email contents after our successful read. Let’s add a cleanup step to our read test:


const superagent = require('superagent')
const mailsac_api_key = process.env.MAILSAC_API_KEY;
const expected_message = 'This is some text from our Selenium test.';
const testInbox = '[email protected]';

  .set('Mailsac-Key', mailsac_api_key)
  .then((messages) => {
      const messageId = messages.body[0]._id
          .get(`${testInbox}/` + messageId)
          .set('Mailsac-Key', mailsac_api_key)
              .then((messageText) => {
                  if (messageText.text !== expected_message)  {
                    throw new Error(`Message to delete '${messageText.text}' does not match expected text '${expected_message}'`)
                    console.log("API Read Op: Message comparison passed");
                    .set('Mailsac-Key', mailsac_api_key)
                    .then((messageResponse) => {
                        console.log(`API Deletion Op: ${messageResponse.body.message}`)
  .catch(err => {


Let’s add it to a test script and our workflow YAML file:

"scripts": {
    "dev": "next dev",
    "build": "next build",
    "start": "next start",
    "lint": "next lint",
    "external-tests": "node tests/external-login.js",
    "test": "node tests/button-render.js && npm run mail-tests",
    "mail-tests": "node tests/email-send.js && node tests/email-read.js",
    "e2e-test": "start-server-and-test dev <http://localhost:3000> test"


Note that we added a run mail-tests script to our end-to-end testing.

Try your end-to-end script locally to ensure it works:

End to end sample test

GitHub Action Test

Now that you have a working test on your local workstation, it’s time to push it up so GitHub Actions can start running your tests. If you haven’t already, read through the first article to catch up on GitHub Actions configuration and initialization.

As a reminder, this is our main.yml workflow file:

on: [push]

    runs-on: ubuntu-latest
    name: Run Selenium Tests
    - name: Start selenoid
      uses: Xotabu4/selenoid-github-action@v2

    - uses: actions/checkout@v1
    - run: npm ci  

    - name: Run end to end tests
      run: npm run e2e-test

    - name: Run external login test
      run: npm run external-tests


With all that said, let’s try and see if this email test sends an email on GitHub.

Do a git push and check your results on GitHub:

A gitHub test failure

Looks like a failure. On closer inspection:

GitHub specific failure with details

Ah, that’s right! We forgot to set our API keys at the GitHub level. Let’s go ahead and do that.

GitHub Actions Secrets

You can find it under Settings in your repo:

Github walkthrough image : Click settings

Then under Secrets → Actions click New repository secret

Add each secret that will be needed:

GitHub Secrets listing for your Actions.

Finally, ensure you add it to the workflow file:

- name: Run end to end tests
      run: npm run e2e-test
        MAILSAC_API_KEY:  ${{secrets.MAILSAC_API_KEY}}
        MAILSAC_HOST:     ${{ secrets.MAILSAC_HOST }}
        MAILSAC_PORT:     ${{ secrets.MAILSAC_PORT }}


Do a git commit and git push and see the results on GitHub:

Successful email test with GitHub actions.

Success! You can check the details to ensure the API read and write options fire fired off:

Github actions success detailed view.


GitHub Actions is a powerful CI/CD tool and we have only scratched the surface of its capabilities with Selenium. We’ve also shown the power of email testing and how you can ensure the contents of every email are intentional.

We hope you enjoyed the guide, and hope to hear from you on our forums or follow our other content on LinkedIn.

10 Best Testing Tools for Software Developers in 2022 Logo

10 Best Testing Tools For Software Developers in 2022

As a software developer, it’s crucial to have effective testing tools. They run the gamut from quick libraries to full-fledged analytic frameworks. They also range from free to paid. But which ones are the best in the testing space? In this article, we will list the top 10 best testing tools for software development teams.

But why test?

We can hear the groaning now. Testing is like exercise. We know we’re supposed to, but only so many of us do. Even fewer of us genuinely enjoy it. But testing doesn’t have to be a grind. In fact, we’re willing to bet a portion of you will enjoy it. Why bother with tests?

  • Testing can be fun – A lot of these tools are automation based. You can focus on crafting a comprehensive test as part of your feature building.
  • Testing can be done by other groups – It can create a bridge between you and, for example, the QA team. Commiserating around shared testing struggles can go a long way in building trust between teams.
  • An investment in yourself – Much like the exercise analogy, an investment in testing is an investment in yourself. Refactoring code, deployment flight checks, and all-around confidence about your changes can only be achieved by proper testing.

Now that you know some of the whys, let’s walk through the 10 best testing tools for software developers.

The 10 Best Testing Tools For Software Developers in 2022

1. Puppeteer 

Puppeteer is a favorite of the NodeJS community due to its easy integration into your existing build system. It automates form submission, UI testing, keyboard inputs, and more. The main limitation it does have surrounds browser support. As of this writing Puppeteer only supports Chrome. Firefox support is still in the experimental phase.

Puppeteer’s killer feature is that it installs the browser binary for you, making integrating it into your build system easy.

We’ve written an article on using Puppeteer to walk through a common testing scenario. It guides through testing a login screen to and ensuring entering a bad password does not allow you to log in. You can find it under Automate the Testing Pain Away with Browser Automation.

2. JMeter 

JMeter is a popular open-source tool that can test web applications, network performance, and more. It has a versatile GUI for manual testing and a CLI for automated testing. It also offers recording capabilities much like some other tools on this list. It’s a powerful tool with one enormous drawback: it can only integrate with Java applications.

3. Selenium WebDriver 

Selenium WebDriver is an open-source automation tool that can test web browsers across different platforms. It’s by far one of the more popular testing tools available around browser automation testing. It can incorporate into a variety of different continuous integration / continuous deployment tools.

Additionally, WebDriver is one of the few tools to be W3C recommended! In their words:

Major browser vendors (Mozilla, Google, Apple, Microsoft) support WebDriver and work constantly to improve the browsers and browser controlling code, which leads to a more uniform behavior across the different browsers, making your automation scripts more stable.

From Selenium’s Project Page
A successful Selenium WebDriver Test

To help you get started with WebDriver we’ve written a guide on creating your automated headless browser testing.

4. Mailsac 

Allow us to shamelessly plug ourselves for a moment, but for your email testing and capture needs, Mailsac is top-notch. We provide just-in-time subdomains and a robust API for automation-driven email testing.

Here’s a guide to using our on-demand subdomain feature to create Company-Wide Email Inboxes

A video walkthrough of using ad-hoc Developer Environments in your testing

5. Postman 

Postman is a flexible tool for managing and automating testing requests. It has an intuitive GUI and can generate scripts in various programming languages. You can also store playbooks in Postman to call later using their collection runner.

postman  test runner
Job Runner CLI Status From Postman’s Writing Tests Blog Post

Postman’s killer feature is the ability to integrate API calls onto your build system: 

postman   travis success
Job Runner CLI Status From Postman’s Writing Tests Blog Post

Give Postman a shot, it’s one of the most popular web API testing tools for a reason.

6. Selenium IDE

Selenium IDE is WebDriver’s GUI-driven sibling. It does a similar job of orchestrating browser functions but with the twist that it can “record” actions as you perform them in your browser.

Successful test suite
Successful test suite

Selenium IDE can test web applications, API endpoints, and everything else that WebDriver can do. It’s available as Firefox, Chrome, and Edge extensions.

Much like WebDriver we’ve written a quick start guide on automating the browser.

7. Chrome DevTools

The built-in Chrome DevTools offer a powerful extension that allows you to inspect and test web pages in real-time. Most other browsers offer this capability but Chrome is hard to beat. It offers:

  • Built-in Lighthouse report capable of grading the accessibility of your page
  • Artificial network throttling to simulate slow connection speeds
  • Performance measurement across pages
  • Hundreds of extra plugins

8. JUnit5 

JUnit5 is a popular open-source unit testing framework that can test Java applications. It offers the ability to have test runners for your test cases and enables you to focus on Test Driven Development.

It even has its own tag on Stack Overflow.

9. Cucumber Open

Cucumber is an open-source testing tool that can be used to test web applications and APIs. Cucumber is a rather unique one on this list in that it focuses on getting the specifications right the first time. It’s called Behavior Driven Development and it allows project managers and technical contributors to collaborate on concrete aspects of the application.

10. Firefox Developer Tools

Firefox does a great job innovating on the developer toolset. (3D View anyone?) Since it can do anything the Chrome DevTool set can, we’ll use this section to focus on specific plugin shoutouts:

User-Agent Switcher

Test your browser detection logic with this extension.


Ghostery is great for a variety of reasons, not least of which is to prevent distractions. It blocks a variety of trackers, ads, and generally improves page performance.

Cookie Manager

A versatile extension that can help you test all sorts of functionality in your application. Cookie Manager can help you with everyday tasks from authentication testing to session switching and inspection. You can additionally export and import cookie sets.


These are some of the best software testing tools available for developers. They all have their strengths and weaknesses, but they are all powerful tools that can help you improve your code quality.

If you’d like to discuss some of the tools you use for your software testing we’ll love to hear about it! Head on over to our community at and discuss your must-have or time-saving tools.

Blog cover

Own Your Software Testing Workflow With Subdomains

When the topic of domains and email comes up most people begin and end the conversation at the top domain level. Subdomains seem to be left out of the conversation in their entirety. Are we trapped in our thinking about subdomains as mere marketing and newsletter features? Maybe it’s too difficult to use subdomains without an IT team involved. Maybe no one has brought up subdomains outside of meme-filled newsletters. Maybe you just haven’t thought about subdomains in general.

Why use subdomains in your testing suite?

Well, let’s break up that thinking. Subdomains have a lot to offer. Do you have trouble testing 10 different email features in your application? Does the thought of accidentally sending an email to thousands of users that says “Test” make you break into a cold sweat? Subdomains can help.

We’ll show you some of the possibilities of subdomains and walk through some use cases. We’ll also provide a quick 15-second walkthrough at the end that will setup up 2 new subdomains for development and testing purposes.

And we’ll do all this using Mailsac’s Zero-Config subdomain feature.

But before we show you some of the juicy scenarios, let’s do a quick rundown of what a subdomain actually is.

What’s the difference between an email domain and a subdomain?

Breaking down what a subdomain really means in an email

Subdomains are a way to slice up domains for specific functions like newsletters and blogs. The advantage of a subdomain is having a clear purpose tied to the name. Receiving emails from [email protected] and [email protected] show their intent from their name alone. Receiving emails from [email protected] and [email protected] is a lot vaguer. The former set clearly sends memes and educational nuggets. The latter could be a friendly name for our billing bots.

Subdomains = an easy way to differentiate email by function.

Alright, sorry about that. Had to make sure everyone was on the same page on subdomains. Let’s move on to 3 different subdomain scenarios.

Subdomain Use Case 1: Developers Get Their Own Email Domains

You work on a team of developers, and each of you needs to test the same features on a few different applications. Additionally, each feature has an email workflow attached to it.  The usual response to this is to have a shared inbox, for example, [email protected]. But the pain around that approach comes fast. Issues like:

  • Difficulty in separating out each developer’s testing scenarios
  • Having to sift through 1000 other unrelated emails while looking for that 1 workflow email is painful
  • Complex workflows are pretty difficult to track
An example of how you can pin an app to a a particular subdomain inbox.
A domain for me, a domain for you

Creating an email subdomain per developer is an effective way to isolate these emails across systems:

Remember that you don’t need to create these inboxes ahead of time. They are made on the fly and removed when they make sense for you, the person knee-deep in the application.

Also not shown above just yet: Mailsac’s unified inbox in action.

Subdomain Use Case 2: Company-Wide Domains per Environment

Example of segmenting via subdomains in your software testing suite.
Ensure emails stay in their zone

Environments for each set of applications are a pretty common scenario amongst enterprises. A sample above shows 2 applications split between 3 environments:

The upside of this approach is having predefined email subdomains for each environment. Developers, QA teams, and operations all know which environment the emails are associated with. QA testers can review the messages easily knowing which environment sent the emails. Operations and developers know which email address and domain to use as variables when configuring tests or environments. Ultimately, this saves time for all the teams involved.

Subdomain Use Case 3: Email Driven API Workflow

An example of how you can use subdomains in targeting specific inboxes in a subdomain.

An email-driven API workflow is a workflow that kicks off when an email arrives. The approach resembles the first scenario, where each developer gets their own domain. The difference is the usernames are less flexible. You pin it once to an API and use it for the long term. For example:

  • An email to [email protected] can trigger a Submit API action that can create a case in the HR management system
  • An email to [email protected] can trigger an Integration API action that can automatically create a ticketing workflow in your Incident Management system.

You can even string together a received email to a webhook using Mailsac’s webhook service. If you’d like to poll for updates instead we have websocket for close to real-time processing or the rest API for polling.

Alright, enough theory let’s do a walkthrough.

Walkthrough: Company-Wide Environments

Using the company-wide scenario we can have a working subdomain in a few seconds using Mailsac. A partner video will walk through the individual developer scenario.

You also have the option of using your own domain. This requires an external domain service provider. There are lots of guides out there on which domain registrar is the best

But let’s make this easy. Let’s use Mailsac’s Zero-Config Subdomain tool and bring up a new subdomain in 2 clicks. Note that you will need at least a Business Plan to make this scenario work. You can still enjoy the benefits of a single subdomain through the Indie Plan.

Zero-Click Subdomain

After creating a Mailsac account, navigate to “Custom Domains” from your dashboard:

Custom subdomain location in Mailsac's dashboard.

Type the name of the subdomain you’d like, in our case acme-dev and acme-test

Custom subdomain location and naming input in Mailsac's dashboard.

And that’s it! You should have 2 custom subdomains ready to use. Let’s put it them rough their paces. We’ll send out these emails from any client (I’ll use Gmail):

  1. To: [email protected]
    Subject: Email sent to Billing (DEV)
    Content: This is meant for dev
  2. To: [email protected]
    Subject: Timesheet Submission (DEV)
    Content: Sample timesheet submission
  3. To: [email protected]
    Subject: Timesheet Submission (TEST)
    Content: Sample timesheet submission
A manual approach to firing off emails to specific inboxes.
Nothing special here, just simulating a programmatic email

After submitting your set of emails, you *could* just check [email protected] and [email protected] individually…

Mailsac inbox where testing emails were directed to.
This is already looking painful…

…or you could use the Unified Inbox feature that displays all of your custom domains, subdomains, and private addresses in one convenient location:

Mailsac's unified inbox tool.
Much better

It’s just that easy!

Wrap Up

With this new superpower, you should be able to conjure up lots of different use cases for subdomains. The friction of creating and importing domains is completely taken care of for you. No need to register a domain with an external registrar, or manage an IT team to handle registration for you.

We’re always looking for feedback, so let us know what you think or if you run into any problems on our forums.

Blog Cover

Automate the Testing Pain Away with Browser Automation

When I say “You need to test your code”, do you wince? Is it a feeling of guilt, one of “I know I should, but…”. Testing may not conjure up the sexiest of images. We as developers frequently put tests off until the end of our feature cycle. Or respond to a production bug by issuing a quick patch. Or worse, just bury our heads in the sand and pretend that we don’t have any bugs in our code at all. (Note: All code has bugs).

The reality is that testing is an incredible investment in your code’s future. Investing in tests is like an insurance policy: hedging your bets against an unknown future. An unknown future consisting of bitrot, dependency deprecations, or service API changes. Testing provides the ability to patch those unknowns through refactoring or flat-out removing stale dependencies. Testing can also buffer against those risks, providing peace of mind.

In this post, I’ll outline 3 different types of testing tools:

  • Selenium WebDriver
  • Selenium IDE
  • Puppeteer

To do an apples-to-apples comparison the testing scenario will be the same for all three tools. I’ll also model my testing after a user’s typical behavior. Behaviors like login attempts, searching, and form submissions. They also try to hit every layer of the application, from the user interface to the database.

Benefits of Testing a User Interface

Testing isn’t just limited to the backend. Testing your interface can provide complete end-to-end testing scenarios such as:

  1. Repeated calls to your modal. Does the modal come back after the first call?
  2. Does your submit button produce an error if the form has an incorrect value?
  3. Does the UI load after a successful login to an empty state in your application?
  4. Does a specific result come back after a form search?

I’m going to walk through a straightforward testing scenario with three tools. Not to rank them, but to touch on the nuances of each. Some of these tools allow you to create tests through simple browsing. Others are headless, allowing you to drive through programming languages.

What’s a headless browser?

Conventional browsing involves rendering forms, buttons, and images to the user. A headless browser interacts with websites through code without displaying any controls. Headless browsing opens up possibilities that are tough to achieve with conventional browsers like:

  • Integration with your build systems
  • Consistency in testing
  • Decreasing the duration of your tests
  • Layout screen captures and comparisons

Tools of the Automated Browser Trade

Onto the good stuff: The tools and testing scenarios.

The Most Popular – Selenium WebDriver

Selenium is by far the most popular testing tool out there. It covers headless testing and both local and remote tests.

WebDriver targets as its core base Developers and QA Team members who can write code.

The Easiest To Get Started with – Selenium IDE

Selenium designed the IDE version for exploratory testing and bug replication. It’s perfect for walking through a bug with someone else or creating a recording of a bug for your ticketing system.

The NodeJS Fan Favorite – Puppeteer

Puppeteer is a favorite of the NodeJS community due to its easy integration into your existing build system. It automates form submission, UI testing, keyboard inputs, and more. It’s main limitation however is the browsers it supports. As of this writing Puppeteer only supports Chrome. Firefox support is, as of this writing, experimental.

Puppeteer’s killer feature is that it installs the browser binary for you, making the integrating into your build system easy.

Testing Scenario: A Failed Login to

Here’s our testing scenario:

  1. Load
  2. Click the “Log in” button
  3. Load a page with “Welcome! – DEV Community” in its title.
  4. Click on the “Continue” button
  5. Ensure an “Unable to login” banner appears on the page.

For consistency throughout the walkthrough, I’ll use:

  1. Chrome as my browser
  2. Javascript as the programming language of choice

Test Case 1 – Selenium WebDriver

Let’s begin with an empty directory and selenium package installation:

npm init tests
cd tests
npm install selenium-webdriver

Next, download a browser driver. You can find the full supported list in selenium’s code repository. You can place the binary anywhere. For this walkthrough, I’ll place it in the current project directory under the bin/ path.

Set your specific browser driver path:

export PATH=$PATH:$PWD/bin

I’ll be using this quick test setup (selenium.js):

const {Builder, Browser, By, Key, until} = require('selenium-webdriver');

(async function example() {
  let driver = await new Builder().forBrowser(Browser.CHROME).build();
  try {
    await driver.get('');
    await driver.findElement(By.linkText('Log in')).click();
    await driver.wait(until.titleIs('Welcome! - DEV Community'), 3000);
    await driver.findElement('commit')).click();
    await driver.wait(until.titleIs(''), 3000);
    let errorBox = await driver.findElement(By.className('registration__error-notice'));
    await driver.wait(until.elementIsVisible(errorBox));
    let errorText = await errorBox.getText();

    if (!errorText.includes('Error')){
      throw new Error(`Error text does not contain expected value: ${errorText}`);

  } finally {
    await driver.quit();

Set your driver and run the file

SELENIUM_BROWSER=chrome node selenium.js
A failed Selenium Test

In general I like to ensure my tests fail from the start, followed by working towards passing the tests:

const {Builder, Browser, By, Key, until} = require('selenium-webdriver');

(async function example() {
  let driver = await new Builder().forBrowser(Browser.CHROME).build();
  try {
    await driver.get('');
    await driver.findElement(By.linkText('Log in')).click();
    await driver.wait(until.titleIs('Welcome! - DEV Community'), 3000);
    await driver.findElement('commit')).click();
    await driver.wait(until.titleIs(''), 3000);
    let errorBox = await driver.findElement(By.className('registration__error-notice'));
    await driver.wait(until.elementIsVisible(errorBox));
    let errorText = await errorBox.getText();

    if (!errorText.includes('Unable to login')){
      throw new Error(`Error text does not contain expected value "${errorText}"`);

  } catch(e) {
    console.error(`Error running test suite: ${e.message}`)
  finally {
    await driver.quit();

With line 15 fixed, rerun the script:

A successful Selenium Test


The above was a taste of what you can do with Selenium. You can even break out of the testing mindset and use Selenium for scraping and populating activity trackers.

On to the next tool.

Test Case 2 – Selenium IDE

While the previous test requires some programming ability, Selenium IDE is friendly to anyone who can drive a browser. The IDE version’s main use case is bug discovery, recording and profiling.

First, download the package from the Selenium page.

After installing the plugin, start a new project:

Selenium IDE introduction screen.
New Project Page
Selenium IDE's project base URL, where all of your tests will start.
Set our base url to

After you hit “Start Recording”, Selenium will launch a new Chrome window and redirect you to

Initial Dev.To Walkthrough with Selenium IDE

From the video, we:

  1. Let the initial page load
  2. Clicked on the “Log in” button
  3. Clicked on the Selenium IDE extension
  4. Stopped the Extension recording
  5. Arrived at the Commands window below
Selenium IDE's properties loaded automatically
Selenium testing properties loaded automatically

To continue our test scenario, let’s ensure that the page title is Welcome! - DEV Community and that our login attempt fails with an empty submission.

Again, I always like to have my tests fail first, so let’s start with that case. Use Selenium’s assert title command to ensure the title is what we expect. Add it to the command list:

Selenium IDE's asserting that the title fails.
Asserting the page title to fail

If you run the test, it should fail:

Failed automation testing in Selenium IDE.
Example of a failed test

Let’s go ahead and fix it with the correct title and rerun the test:

Successful Title Check

And success! Now let’s add the login check:

Walking through a complete test to success.

To summarize the video, we:

  1. Started a new recording
  2. Hit the Log in button
  3. Clicked Continue without supplying credentials
  4. Used the Selenium element picker to pick out the element we were interested in asserting.

The Commands window should now look like this:

Successful automation testing in Selenium IDE.
Added Command Check


The IDE version is the simplest to get started with and I recommend it for initial test write-ups. It can help you identify which elements you need to test against, think about app flow and what counts as a failure.

One question remains: Rendering the browser is nice, but I want to hook this into my continuous integration system. How can I do that when every test wants to load an application that requires a windowing system?

The answer is to go headless.

Test Case 3 – Puppeteer

Puppeteer is the perfect match to test web UI components inside a continuous integration system. It’s fast, headless, brings its own dependencies and runs the latest versions of Chrome and Firefox.

Let’s start by installing puppeteer on a new project:

mkdir tests
npm i puppeteer

Keep in mind that this automatically installs the chrome driver we had to manually download in the Selenium example. From Puppeteer’s documents:

When you install Puppeteer, it downloads a recent version of Chromium (~170MB Mac, ~282MB Linux, ~280MB Win) that is guaranteed to work with the API (customizable through Environment Variables).

With that said, let’s create a test file that will run (and fail) our test scenario (puppeteer.js):

const puppeteer = require('puppeteer');

(async () => {
  const browser = await puppeteer.launch({headless: false});
  const page = await browser.newPage();
  const loginSelector = 'a[href="/enter"]';
  const submitLoginSelector = '[name="commit"]';
  const errorBoxSelector = '.bad notice';
  try {
    await page.goto('');
    await page.waitForSelector(loginSelector,{ timeout: 3000 });
    const pageTitle = await page.title();

    if (pageTitle !== 'Welcome! - DEV Community'){
      throw new Error(`Page title ${pageTitle} does not match expected value`);
    await page.waitForSelector(submitLoginSelector,{ timeout: 3000 });
    await page.waitForSelector(errorBoxSelector,{ timeout: 3000 });
    console.error(`Error in test suite: ${e.message}`)
  }finally {
    await browser.close();
Failed test due to incorrect error box selection

Some notes on the above code:

  • Lines 6-8 are Puppeteer’s method of selecting elements on the page.
  • Like Selenium WebDriver, you have to manually check a page’s attributes and decide on what to do should they fail
    • In the above code it’s line 15, asserting the title matches the expected value
    • It’ll also implicitly fail on line 20, due to the error div class not matching what sends to the browser.
  • I’ve disabled the headless feature to show that Puppeteer lets you do that!

Let’s fix the test. Change it to the correct value *and* turn on headless mode:

const puppeteer = require('puppeteer');

(async () => {
  const browser = await puppeteer.launch({headless: true});
  const page = await browser.newPage();
  const loginSelector = 'a[href="/enter"]';
  const submitLoginSelector = '[name="commit"]';
  const errorBoxSelector = '.registration__error-notice';
  try {
    await page.goto('');
    await page.waitForSelector(loginSelector,{ timeout: 3000 });
    const pageTitle = await page.title();

    if (pageTitle !== 'Welcome! - DEV Community'){
      throw new Error(`Page title ${pageTitle} does not match expected value`);

    await page.waitForSelector(submitLoginSelector,{ timeout: 3000 });
    await page.waitForSelector(errorBoxSelector,{ timeout: 3000 });
    console.error(`Error in test suite: ${e.message}`)
  }finally {
    await browser.close();

Now rerunning the test simply gets you the empty prompt:

tests:DreamMachine % node puppeteer.js
tests:DreamMachine % 

Nice, simple, and clean.


I’ve gone through three different sets of tools for different needs. The best part about these tools is that you can string them all together or pick and choose the ones that are right for you.

I hope the main takeaway is the same: Testing can be painless and even fun!

Selenium can also be used to test email signups with Mailsac.

Questions or comments? Stop by the Mailsac Forums, we’d love to hear from you!

Blog Cover

Guide To Stress Free Email Testing with Next.js

Developing an application that sends emails is straightforward but not without its risks. Ensuring deliverability but not actually having any of those emails land inside real inboxes is a top concern for any developer. Which leads to questions like: “How do you test your application’s outbound email capabilities?” or “How do I manage email testing for free?”

Enter email capture services. While the term “email capture service” tends to focus on the marketing aspects (capturing information from your calls to action, ensuring emails don’t get caught in spam, etc) they also include SMTP deliverability. Mailsac offers an email capture service that addresses the deliverability aspect, specifically not delivering any email to its intended recipient. Effectively a “black hole” where no email should escape to the outside world.

In this post, we’ll walk through a sample application in Next.js that will generate emails and have those emails captured by Mailsac’s email sandboxing service.

Do I Really Need To Do Email Testing?

Some frameworks do come with email previewing capabilities like Rails’ ActionMailer. Said frameworks don’t actually attempt to send anything but instead preview the email on your machine. We recommend real testing during the development and quality assurance phase by using an external SMTP server to mimic the application’s behavior in production.

Testing that capability has to be done safely unless you want to land on Twitter’s trending page for accidentally sending customers an integration test email.

Test Email Sending With A Next.js Application

For the rest of this guide, we’ll focus on wiring up a simple application that will allow users to send an email when a button is pushed from a UI. We’ll then demonstrate the capture of those emails in our development environment.

The components we’ll use are:

Application Creation

While the focus of this guide isn’t a line-by-line walkthrough of the sample code, we’ll focus on the key aspects of the application that mainly involve emailing capabilities.

The application source can be found in our git repository.

1. Application setup

Let’s start by creating a quick next app with tailwind support:

mailsac % npx create-next-app
Success! Created nodejs-send-email at /Users/mailsac/code/nodejs-send-email

cd nodejs-send-email
npm install -D tailwindcss postcss autoprefixer @tailwindcss/forms
npm install @headlessui/react@latest @heroicons/react
npx tailwindcss init -p

The above is the recommended way to install tailwind on Next.js according to their guide.

Configure tailwind.config.js by adding the highlighted lines:

module.exports = {
  content: [
  theme: {
	extend: {},
  plugins: [

and then add tailwind itself to the global CSS file inside styles/global.css and comment out some default CSS created by npx:

/* @media (prefers-color-scheme: dark) {
  html {
    color-scheme: dark;
  body {
    color: white;
    background: black;

@tailwind base;
@tailwind components;
@tailwind utilities;

Tailwind is strictly optional but recommended for easy styling of the frontend.

2. Add the front page UI

Feel free to add your custom frontend code or use the index.js and components/notifications.js react component samples inside our repo.


import { useEffect, useState } from "react";
import Notification from "../components/notifications";

export default function Index() {
  const [sentEmail, setSentEmail] = useState(false);
  const [emailTo, setEmailTo] = useState("");
  const [emailBody,setEmailBody] = useState("");
  const [resultMessage, setResultMessage] = useState("");

  const sendEmail = () => {

  useEffect( () => {
      method: 'POST',
      body: JSON.stringify({ to: emailTo, body: emailBody})
    .then( res => res.json())
    .then(response => {
    .catch(error => console.log(error));    


  const SentEmailBanner = sentEmail === true? <Notification message={resultMessage} /> : null;

The second line brings in a component that takes in a message and formats it as a pop-up notification. The useEffect() method sends your email recipient and body input to the backend, which will forward that data to Mailsac’s servers.

3. Sign up for Mailsac’s Email Capture

Mailsac has a free email capture service. All you need is to sign up for an account and generate a key:

Mailsac dashboard
Mailsac Dashboard

4. Add a backend mail handler route

Once you’ve generated and saved your keys, you can place them in a .env file:


MAILSAC_API_KEY=Key generated from above

Following our email capture documentation, we’ll create a backend API route for Next to handle the request:


const nodemailer = require("nodemailer");

export default async function handler(req, res) {
  let emailEnvelope = JSON.parse(req.body)
  if (
        req.method === 'POST' 
        && typeof( !== 'undefined' 
        && !== ''
    const mailsaUserName = process.env.MAILSAC_USERNAME
    const mailsacAPIKey  = process.env.MAILSAC_API_KEY
    const transporter = nodemailer.createTransport({
      host: '',
      port: 5587,
      // will use TLS by upgrading later in the connection with STARTTLS
      secure: false,
      auth: {
        user: mailsaUserName,
        pass: mailsacAPIKey
    try {
      const results = await transporter.sendMail({
        from: '"Sample App" [email protected]',
        subject: 'Sample App Send',
        text: emailEnvelope.body
          message: "You should now see an email in Mailsac's capture service", 
    } catch (error){
      console.log(`ERROR ${error}`)
      res.status(500).json({ message: `${error.response}`, response: error })
  } else {
    return res.status(200).json({message: "No data"});

In the highlighted line, we’re ensuring the useEffect() hook gets called with input data before we allow the rest of the function to continue. useEffect() gets called a variety of times in the component lifecycle, and this check is to ensure it was initiated by an end user and not as part of the component mounting.

5. Test driving the app

Fire up the application via

npm run dev

Navigate to http://localhost:3000 and type a text message:

Walking through our sample application form.

Then navigate over to to view the message

Checking the inbox at

6. Capturing other email domains

While that works well as a contrived example, the real value comes when using any arbitrary email in the recipient field:

Full application walkthrough demo, with a free check at mailsac.

Capturing emails outside the domain is extremely valuable when switching between different environments. For example, in the demo application example above, the .env environment file could instead look like


With the updated send-email.js

const nodemailer = require("nodemailer");

export default async function handler(req, res) {
  let emailEnvelope = JSON.parse(req.body)
  if (
        req.method === 'POST' 
        && typeof( !== 'undefined' 
        && !== ''
    const mailsaUserName = process.env.MAILSAC_USERNAME
    const mailsacAPIKey  = process.env.MAILSAC_API_KEY
    const transporter = nodemailer.createTransport({
      host: process.env.MAILSAC_HOST,
      port: process.env.MAILSAC_PORT,
      // will use TLS by upgrading later in the connection with STARTTLS
      secure: false,
      auth: {
        user: mailsaUserName,
        pass: mailsacAPIKey
    try {
      const results = await transporter.sendMail({
        from: '"Sample App" [email protected]',
        subject: 'Sample App Send',
        text: emailEnvelope.body
          message: "You should now see an email in Mailsac's capture service", 
    } catch (error){
      res.status(500).json({ message: `${error.response}`, response: error })
  } else {
    return res.status(200).json({message: "No data"});

The above edits would allow you to deploy to a testing or production environment and the only changes required would be in the .env file. Specifically, the SMTP host and authentication settings.


The above guide just scratches the surface of what you can do with our email services. We provide a unified inbox that allows testers to view their bulk email testing in one unified view and custom domains for those who do not have their own domains with zero setup configurations.

Additionally, we have a guide on using both custom domains and a unified inbox in your system testing. Check it out and tell us what you think on our forums!

Using Selenium To Test Account Email Signups

All the code shown in this article is published at

Selenium and Mailsac can be used to test the delivery and contents of a signup email sent by a web application.

This example will demonstrate how to configure Selenium and provide code examples to automate and integrate testing with Mailsac.

What is Selenium?

Selenium is an automation tool for testing website user interfaces. It is open-source and supports multiple programming languages such as Java, Python, Javascript etc.

Selenium is not a single tool but is composed a several tools. Our example will focus on the WebDriver component. This will allow us to test our application as if a real person were operating the web browser.


Installing Selenium

The Selenium WebDriver is installed during step 2 by running npm install.

  1. Clone the selenium-js-example repository and change directories to the cloned repository
    git clone && cd ./selenium-js-example
  2. Install the Selenium WebDriver by running npm install
  3. Download browser driver for the browser that will be tested (see table for download links).
  4. Place the browser driver in the system PATH
Internet ExplorerIEDriverServer.exe

The safaridriver is included with Safari 10 for OSX El Capitan and macOS Sierra. It does require Remote Automation in the Develop Menu to be enabled.

Configure the Browser for Selenium to Use

This example will default to using Firefox. In order to use a different browser set the SELENIUM_BROWSER environment variable.

List of supported SELENIUM_BROWSER values


Web Application Overview

The example web application consists of a single page with a form. The form accepts a username and email address.

Configuring the Web Application

Email will be sent using the Mailsac Outbound Message REST API. You will need to update mailsacAPIKey with your API keymailsacFromAddress is the address that this example will use are the from address.

const mailsacAPIKey = ""; // Generated by mailsac. See
const mailsacFromAddress = "[email protected]";

Manual Test of Email Delivery

To manually test email delivery, launch the example web application by running npm start from the command line. Use a web browser to view http://localhost:3000/index.html

  1. Enter a username and email address.

2. If everything went well you should see a confirmation.

3. Check the inbox of Mailsac address you send to using the form on

4. Verify the message you sent has been received.

Automated Testing Using Selenium

To automate UI testing a few different components are required:

  • Selenium WebDriver: Automates input into our web application’s form
  • Mocha: Test framework to run the tests
  • HTTP Requests Module: To interact with the Mailsac API
  • Assert Module: Validates if a given expression is true
  • Webserver: Runs our web application

All of these components are installed when running npm install

Configure Mailsac API Key

To interact with the Mailsac API an API Key is needed. To generate a new API Key sign in to Mailsac and go to the API Keys Page.

An API Key is available for free to all registered users of Mailsac.

Configure the test to work with your API Key by adding it to the following line in ./test/test.js

const mailsacAPIKey = ""; // Generated by mailsac. See

Run the Test

Before running the tests your Mailsac API key needs to be configured in ./test/test.js and SMTP settings configured in app.js.

The tests can be executed by running npm test from the command line.

npm test

> [email protected] test /home/user/repos/selenium-js-example
> mocha

    register new user
(node:838754) [DEP0066] DeprecationWarning: OutgoingMessage.prototype._headers is deprecated
      ✓ sends email with link to website (1383ms)

  1 passing (1s)

The last line in the above code snippet 1 passing (1s) shows our test passed. If the test failed, an error message will be displayed.

If you are using a browser other than Firefox you will need to add an environment variable when running the tests (eg SELENIUM_BROWSER=chrome npm test).

Using Mocha and Selenium to Automate Tests

This section will cover how Mocha and Selenium work together in this code example to test email delivery.

The integration tests are located in ./test/test.js. The tests are written in Mocha, which uses a behavior driver development model. This allows for the description of tests in easy to understand language.

Mocha Test Introduction

In the following example, the describe block includes a description of what is being tested. The it block describes the expected result. assert is used to test the for truth. If the expected statement is not true, there will be an exception, and the test will fail.

describe("tests truth", () => {
    it('true equals true', function() {
        assert(true); // assert checks for truth
    it('false equals false', () => {
        // assert equal checks the first and second parameter are equal

Mocha and Selenium

This section is a line by line explanation of the Mocha tests in the example. The code example is available on GitHub.

Mocha is used to call the Selenium WebDriver to perform actions on the example Web Application. The describe block shows we are going to be testing the process of registering a new user. The it block tells us what we expect to happen.

Inside the it block Selenium WebDriver is instructed to:

  • open a web browser using the webapp’s localhost URL
  • find the html element with the id username and enter text in the field
  • find the html element with the id email and enter specified text in the field
  • find the html element with the id submitUserCreation and click on it
it("sends email with link to website", async () => {
  await driver.get(webappUrl);
  await driver.findElement("username")).sendKeys("webdriver", "ExampleUser");
  await driver.findElement("email")).sendKeys("webdriver", signupEmailAddress);
  await driver.findElement("submitUserCreation")).click();

Our webapp will then email the address submitted by Selenium.

There is a for loop, following the Selenium commands, that uses the Mailsac API to fetch the mail from the specified email address. If an email isn’t found, it will retry 10 times waiting about 5 seconds between tries.

let messages = [];
for (let i = 0; i < 10; i++) {
   // returns the JSON array of email message objects from mailsac.
   const res = await request("")
           .set("Mailsac-Key", mailsacAPIKey);
   messages = res.body;
   if (messages.length > 0) {
   await wait(4500);

If no messages are received from the Mailsac API after 10 tries, assert will create an exception and throw the error Never received messages!. The contents of the email are checked to see if the link is in the email. If, the link is not found, an exception is created stating Missing / Incorrect link in email

assert(messages.length, "Never received messages!");
const link = messages[0].links.find((l) => "");
assert(link, "Missing / Incorrect link in email");

Next Steps

This example can be modified to automate your team’s UI testing procedures. For another example of Mocha tests using Mailsac see the Integration Tests Blog Post.

Our forums are a great place to discuss usage of Mailsac’s API.

Github repository for all source code in this example: