Hello friend! As a seasoned quality assurance expert with over 10 years of experience testing complex browser-based apps, I‘m thrilled to walk you through Testing Library Jest DOM.
I‘ve used this incredible tool to effortlessly test UIs across various JavaScript web projects – from React SPAs to Angular dashboards.
Read on as I share my insights from extensive real-world usage to help you master Testing Library Jest DOM.
What is Jest DOM and Why Use It?
Jest DOM is a lightweight JavaScript testing utility that extends Jest, a widely-used JS testing framework, with custom matchers and helpers aimed at simplifying DOM testing.
Here are the key reasons I recommend using Jest DOM:
✔️ Intuitive custom assertions for querying DOM elements based on visible text, accessibility roles, attribute values etc. This allows for more stable tests focused on what users see rather than internal implementation details.
✔️ Helpers for simulating browser events like clicks, scrolls, text entries within Jest tests removing need for a full browser automation solution.
✔️ Utilities for handling async UI updates like waitForElement() and waitForDomChange() to test timing-related issues easily.
✔️ Encourages test designs centered around user interactions rather than implementation specifics. This results in faster test creation and improved maintainability.
Over the last decade testing UIs across various environments, I‘ve found Jest DOM to be invaluable thanks to these factors. Let‘s explore them in more depth.
Top 10 Custom Matchers for Easier DOM Testing
Based on extensive usage through my web testing career, these custom assertions are my go-to picks for simplified DOM testing with Jest:
// 1. Check if element exists in DOM
expect(getByText(‘Submit‘)).toBeInTheDocument();
// 2. Check if element is visible
expect(getByText(‘Submit‘)).toBeVisible();
// 3. Check if checkbox or radio selected
expect(getByLabelText(‘Remember Me‘)).toBeChecked();
// 4. Check if element contains text
expect(getByTestId(‘message‘)).toHaveTextContent(‘Saved‘);
// 5. Check if element has attribute
expect(getByAltText(‘Logo‘)).toHaveAttribute(‘src‘, ‘logo.png‘);
// 6. Check if element contains a class
expect(getByText(‘Submit‘)).toHaveClass(‘btn-primary‘);
// 7. Check if input field or form is valid
expect(getByTestId(‘email‘)).toBeValid();
// 8. Check input/form values
expect(Form).toHaveFormValues({
email: ‘[email protected]‘
});
// 9. Check if element is disabled
expect(getByText(‘Submit‘)).toBeDisabled();
// 10. Check if element is empty
expect(getByTestId(‘cart‘)).toBeEmpty();For a complete reference of 40+ Jest DOM custom assertions, refer to the Jest DOM documentation.
Let‘s now see these matchers in action testing a sample React application.
Testing React Apps Using Jest DOM
As an experienced React QA specialist, I highly recommend using Jest DOM for simplified testing of React component interactions and behavior.
Here is an example workflow:
Step 1: Install Jest DOM and React Testing Library
npm install --save-dev @testing-library/jest-dom @testing-library/react Step 2: Import Jest DOM into Test File
import ‘@testing-library/jest-dom‘; This enables all the custom assertions globally.
Step 3: Render React Component Under Test
Use React Testing Library‘s render method:
import { render } from ‘@testing-library/react‘;
test(‘renders login form‘, () => {
const { getByText } = render(<LoginForm />);
// ... Rest of test ...
});Step 4: Interact & Assert Using Jest DOM Matchers
test(‘login successful‘, async () => {
const { getByText, getByTestId } = render(<LoginForm />);
fireEvent.change(getByTestId(‘email‘), {
target: { value: ‘[email protected]‘ }
});
fireEvent.click(getByText(‘Submit‘));
expect(getByTestId(‘response‘)).toHaveTextContent(‘Login successful!‘);
}) This allows testing React component behavior through simple yet powerful assertions focusing on elements visible to the user.
For an in-depth React testing guide refer to How To Test React Components with Jest and React Testing Library.
Key Benefits of Using Testing Library Jest DOM
As an experienced QA expert having tested UIs across various environments – from startups to Fortune 500 enterprises – here are the major benefits I’ve realized from using Testing Library Jest DOM extensively:
1. Improved Test Readability
The custom matchers clearly communicate test assertions using natural language centered around elements visible to the user:
expect(getByText(‘Submit‘)).toBeDisabled(); At a glance, anyone can grasp the intent behind this assertion.
2. Less Brittle Tests
The custom assertions query elements based on visible UI content rather than internal implementation details.
For example:
expect(getByLabelText(‘Remember Me‘)).toBeChecked() So changes in underlying implementations are less likely to break such integration style tests improving maintainability.
3. Streamlined Async UI Updates Testing
Utilities like waitForElement() and waitForDomChange() simplify testing tricky asynchronous DOM updates and timing issues.
4. Concise Yet Powerful Assertions
Matchers like toHaveFormValues() allow asserting state across multiple form fields succinctly improving test verbosity.
Let‘s now look at some expert-level tips and patterns I utilize working with Jest DOM.
Pro Tips and Best Practices
From comprehensive Jest DOM usage across diverse test automation initiatives, here are 5 key strategies I highly recommend:
1. Create Reusable Custom Helpers
Wrap common assertions into reusable helper functions improving test verbosity:
// helpers.js
export function expectHasError(element) {
expect(element).toHaveClass(‘error‘);
expect(element).toHaveTextContent(‘Error!‘);
}
// Usage
test(‘display error on invalid input‘, () => {
const { getByTestId } = render(<Form />);
expectHasError(getByTestId(‘input‘));
});2. Follow Given-When-Then Structure
Organize tests using given-when-then structure improving comprehension:
describe(‘Login‘, () => {
it(‘login successfully‘, () => {
// Given - Setup
render(<LoginForm />)
// When - Perform action
fireEvent.submit(loginForm)
// Then - Assert outcome
expect(response).toHaveTextContent(‘Success‘);
});
}); 3. Create Reusable Page Objects
Encapsulate selectors and test logic around pages and components into reusable page object classes:
class LoginPage {
constructor() { }
get emailInput() {
return getByTestId(‘email‘);
}
async submitValidCredentials() {
// ... Logic to fill and submit form
}
}
// Use in test:
const loginPage = new LoginPage();
loginPage.submitValidCredentials(); This improves maintenance with cleaner tests.
4. Follow Testing Pyramid
Complement Jest DOM integration tests with isolated unit tests around functions and classes catching bugs early.
5. Use Real Browsers And Devices
While Jest DOM simplifies browser simulation, tools like Selenium and real device clouds enable testing complex real-world interactions across browsers like Safari, Edge and devices which Jest can‘t replicate.
Now that you‘ve seen Testing Library Jest DOM capabilities in action, let‘s summarize everything we‘ve covered.
Key Takeaways and Next Steps
Over the course of this comprehensive Jest DOM guide, we went through:
✔️ Introduction to Jest DOM including its capabilities and why it simplifies browser DOM testing
✔️ Custom Jest DOM matchers with examples demonstrating simplified assertions centered around visible UI
✔️ Workflow for testing React component behavior and interactions using Jest DOM
✔️ Benefits of using Jest DOM from increased test readability to easier async UI testing
✔️ Pro tips I use working with Jest DOM like abstracting logic into helpers and page objects
Hopefully this gives you a solid understating of how Jest DOM can effortlessly enhance testing experience around exercising and asserting against browser DOM elements.
Here are some next things you can do:
🔼 Refer to TestingJavaScript.com for the latest Jest DOM versions, API docs etc.
🔼 Check out my other advanced web testing articles and tutorials
🔼 Try Jest DOM hands-on with sample React apps to get comfortable
Reach out by email anytime if you have any further questions!
Happy testing!
Regards,
John
