Hi there! As you build impressive web applications using JavaScript, thorough testing is what stands between your product and success.
But testing is complex. Where do you start? What should you test? How much? This comprehensive guide has you covered with actionable tips and recommendations.
Why Test JavaScript Code?
Let‘s first understand why testing JavaScript code matters:
1. Catches bugs early
Bugs that reach production incur higher cost. Solid tests catch issues much earlier in development.
Research by Stripe found bugs that made it to production were 15x more expensive to fix than caught during development.
2. Enable safe refactoring
Refactoring improves code quality. But changing working code has risk. Tests allow refactoring with confidence nothing breaks.
According to StackOverflow‘s 2022 survey, 80% of developers leverage tests to safeguard against regressions when refactoring.
3. Improve reliability
Comprehensive tests ensure new changes don‘t impact existing flows. This leads to reliable apps.
A 2022 BlazeMeter survey found 60% of organizations experienced production issues due to lack of testing.
Clearly, testing provides tremendous value. But what exactly should you test and how? Let‘s explore JavaScript testing best practices.
An Overview of JavaScript Testing Types
There are a few testing styles to be aware of:
-
Unit Testing – Focuses on testing individual functions/modules in isolation. Uses mocks/stubs to remove external dependencies. Checks core logic and output.
-
Integration Testing – Verifies interactions and communication between modules. Tests modules together as a group. Real databases and APIs may be leveraged.
-
Functional Testing – Treats the application as a black box. Simulates user stories and workflows from end to end.
-
Performance Testing – Checks responsiveness and speed by simulating expected production load. Identifies bottlenecks.
-
Accessibility Testing – Validates compliance with accessibility standards and support for assistive technologies.
Later sections dive into specific practices for these testing styles. First, let‘s go over some cross-cutting best practices applicable to all JavaScript testing.
Top 10 Cross-Browser JavaScript Testing Best Practices
Whether writing unit tests, end-to-end workflow tests or anything in between, adhere to these vital practices:
1. Structure Tests for Readability
Well-structured test code improves comprehension, debugging and reduces maintenance overhead:
Group related test cases
describe(‘Registration‘, () => {
describe(‘when registering as a new user‘, () => {
it(‘creates a new user record‘);
});
}); Write descriptive test names
it(‘fails validation if password too weak‘);2. Mock External Dependencies Judiciously
Limit mocks to focus test logic and avoid slow tests:
// Mock heavy API call
network.get = jest.fn();But don‘t overmock, or hides real issues!
3. Follow Consistent Naming Conventions
Use intention-revealing names for variables, tests and helpers:
userRepository = new UserRepository();
test(‘user can reset forgotten password‘);
function loginUser() {
// logs user in
}4. Practice Defensive Coding
Handle edge cases and invalid input data:
it(‘handles extremely long input‘);
it(‘trims whitespace from input‘);Write negative test cases too!
5. Test One Component per Test Case
Testing multiple components at once causes confusion on failures:
Bad:
it(‘submits form and shows alert‘);Good:
it(‘submits form‘);
it(‘shows alert on submit‘); 6. Utilize Test Parametrization
Parameterize instead of duplicating tests:
const testInputs = [
{input: ‘valid‘, expected: true},
{input: ‘invalid‘, expected: false}
];
test.each(testInputs)(‘correctly handles $input‘, ({input, expected}) => {
// Assertions here
});7. Incorporate Test Reporters
Use reporters to aggregate, visualize and monitor test executions:
Popular examples include Mocha, Jest, Cypress Dashboard.
8. Practice Cross-Browser Testing
Run tests across environments using services like BrowserStack. 2000+ browser/OS combinations supported.
9. Enable Test Automation
Automate test execution for efficiency using GitHub Actions, Jenkins etc.
10. Follow TDD/BDD Techniques
Write tests first with TDD (Test Driven Development) or specify expected behaviors first with BDD (Behavior Driven Development).
With those vital tips covered, let‘s get into unit, integration and end-to-end specific testing practices.
Unit Testing Best Practices
Unit testing focuses on functionality of individual modules in isolation.
Use mocks effectively – Stub network requests or complex logic irrelevant to core logic under test. But don‘t overmock.
// Testing module that saves user
userDB.save = jest.fn(); // Stub DB
saveUser(input);
expect(userDB.save).toBeCalledWith(input); // Assert save calledTest edge cases – Provide invalid, unexpected and odd inputs:
function parseInput(input) {
// Parses input
}
test(‘handles extremely long input‘, () => {
// Arrange
const veryLongInput = // 1000 chars
// Act
parseInput(veryLongInput);
// Assert
// Logic still works
});Use helpers cautiously – Unit test setup/teardown logic best kept simple and easy to follow. Avoid overusing implicit helpers and hooks:
beforeAll(() => {
// BAD: Complex test environment setup
});
function login() {
// Unit test login helper
}
test(‘logs user in‘, () => {
login(); // AVOID: Implicit helper hides logic
});Integration Testing Best Practices
Integration testing verifies modules cooperate correctly. External services are real.
Validate workflows from module to module – Instead of individual units, test interaction:
test(‘user login workflow‘, async () => {
// Call actual service methods in sequence
const user = await userService.register({/*...*/});
await authService.login(user.email, ‘1234‘);
// Assert
expect(authService.user).toBe(user);
});Practice service virtualization – Mock external vendor services like payment gateways to prevent dependency:
const { fake } = Faker; // Service virtualizer
fake(‘app.paymentGateway‘, methods);
test(‘checkout workflow‘, () => {
// Call fake paymentGateway instead
});Use database sanitization – Insert test data safely into shared database:
beforeAll(async () => {
await db.bulkInsert(‘TestFixtures‘);
});
afterAll(async () => {
await db.cleanup();
});End-to-End & Functional Testing Practices
Validating complete front to backend scenarios from real user‘s perspective.
Follow page object model – Represent UI pages as objects hiding complex selectors from tests:
// Page fragment objects
const LoginPage = {
emailField: ‘#login-email‘,
passwordField: ‘#login-password‘,
submitLogin: () => { /***/ },
};
test(‘user can login‘, () => {
LoginPage.submitLogin();
}); Utilize data driven testing – Parameterize instead of duplicate workflows:
| password | isValid | |
|---|---|---|
| [email protected] | somepassword | false |
| [email protected] | 123validpw | true |
// Import test data
test.each(testScenarios)(‘login with credentials‘, (testData) => {
const { email, password, isValid } = testData;
loginPage.login(email, password);
expect(app.validUser).toEqual(isValid);
});Practice resilience testing – Simulate real-world edge cases – slow networks, server failures:
test(‘handles network failure‘, {
plugins: {
throttleNetwork: true
}
}, async () => {
// Interact with app
// Network randomly fails
await page.waitForResponse();
});Follow accessibility standards – Validate compliance with standards like WCAG 2.1:
it(‘has visible focus styles‘, async () => {
const results = await analyseForAccessibility(page);
expect(results).toHaveNoViolations();
}); Conclusion
Testing JavaScript code thoroughly is invaluable for building successful applications. While it may seem tedious, the effort pays dividends through added confidence, reliability and reduced issues reaching real users.
I hope these comprehensive unit, integration and end-to-end testing tips help you advance your JavaScript testing skills. Feel free to reach out if any questions pop up on your journey to JavaScript testing mastery!
