Cypress API Testing: A Beginner’s Guide
When we think of Cypress, we often associate it with powerful end-to-end testing of web applications. However, Cypress is also a highly capable tool for API testing, allowing developers and testers to validate backend services with ease. In fact, Cypress’s rich syntax, built-in assertions, and asynchronous nature make it an excellent choice for verifying RESTful APIs alongside UI tests or as standalone tests.
In this beginner’s guide, we’ll walk you through the basics of API testing with Cypress, including setup, sending requests, validating responses, and best practices.
Why Use Cypress for API Testing?
Cypress is known for:
Easy installation and setup
Automatic waiting and retrying
Fluent syntax for chaining commands
Real-time debugging through the Cypress Test Runner
While other tools like Postman or REST Assured are popular for API testing, Cypress is great if:
You want to test APIs alongside your frontend
You prefer a JavaScript-based testing framework
You need real-time, browser-based feedback
Setting Up Cypress
To begin, install Cypress in your project:
bash
npm install cypress --save-dev
Open the Cypress Test Runner:
bash
npx cypress open
You can now create test files inside the cypress/e2e/ folder, for example:
api-tests.cy.js.
Writing Your First API Test
Let’s say we want to test a simple GET API from a sample service:
javascript
describe('GET API Test', () => {
it('should return a list of users', () => {
cy.request('https://reqres.in/api/users?page=2').then((response) => {
expect(response.status).to.eq(200);
expect(response.body).to.have.property('data');
expect(response.body.data).to.be.an('array');
});
});
});
The cy.request() command sends a request to the API and returns a response. Cypress automatically handles asynchronous behavior, so there’s no need for async/await.
POST Request Example
You can test POST requests by including a body payload:
javascript
describe('POST API Test', () => {
it('should create a new user', () => {
cy.request({
method: 'POST',
url: 'https://reqres.in/api/users',
body: {
name: 'John',
job: 'Developer'
},
headers: {
'Content-Type': 'application/json'
}
}).then((response) => {
expect(response.status).to.eq(201);
expect(response.body).to.have.property('name', 'John');
});
});
});
This example tests a typical user creation endpoint and verifies the response status and data.
Passing Tokens and Headers
For APIs that require authentication:
javascript
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Edit
cy.request({
method: 'GET',
url: '/api/protected/data',
headers: {
Authorization: `Bearer ${Cypress.env('token')}`
}
});
Store tokens or secrets using Cypress environment variables (cypress.env.json) for security and reusability.
Chaining UI and API Tests
One of Cypress’s strongest advantages is combining UI and API tests in one flow. Example:
javascript
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Edit
cy.request('POST', '/api/login', {
username: 'admin',
password: 'admin123'
}).then((resp) => {
window.localStorage.setItem('token', resp.body.token);
});
cy.visit('/dashboard');
This allows you to simulate logged-in users and test UI behavior based on API interactions.
Best Practices
Use fixtures for managing test data.
Validate response time for performance checks.
Separate API tests into different files or folders for organization.
Use Cypress commands to create reusable API logic.
Don’t mix too many UI and API assertions in a single test.
Final Thoughts
Cypress is more than just a UI testing tool — it’s a complete testing solution that supports robust and reliable API testing. Whether you're validating backend services, performing integration tests, or mocking responses for frontend tests, Cypress provides a simple yet powerful way to ensure your APIs work as expected. For teams already using Cypress for UI testing, adding API tests is a natural and efficient next step.
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