JSON fixture files in Cypress - Build an Automation Script

Verify user login using JSON fixture data

Preconditions (2)

Step 1: Open the login page at 'https://example.com/login'.

Step 2: Load the 'user.json' fixture file containing username and password.

Step 3: Enter the username from the fixture into the username input field with id 'username'.

Step 4: Enter the password from the fixture into the password input field with id 'password'.

Step 5: Click the login button with id 'loginBtn'.

Step 6: Verify that the URL changes to 'https://example.com/dashboard'.

Step 7: Verify that a welcome message with id 'welcomeMsg' contains the username from the fixture.

✅ Expected Result: User is successfully logged in and redirected to the dashboard page with a welcome message showing the username.

Automation Requirements - Cypress

Assertions Needed:

URL should be 'https://example.com/dashboard' after login

Welcome message should contain the username from the fixture

Best Practices:

Use cy.fixture() to load JSON data

Use data-driven selectors with IDs

Use explicit assertions with should()

Avoid hardcoding credentials in test code

Automated Solution

Cypress

describe('Login Test with JSON Fixture', () => {
  beforeEach(() => {
    cy.visit('https://example.com/login');
  });

  it('logs in using credentials from fixture', () => {
    cy.fixture('user.json').then((user) => {
      cy.get('#username').type(user.username);
      cy.get('#password').type(user.password);
      cy.get('#loginBtn').click();

      cy.url().should('eq', 'https://example.com/dashboard');
      cy.get('#welcomeMsg').should('contain.text', user.username);
    });
  });
});

This test uses Cypress to automate login using data from a JSON fixture file named user.json. The beforeEach hook opens the login page before each test. Inside the test, cy.fixture('user.json') loads the JSON data asynchronously. Then, it types the username and password into the input fields identified by their IDs. After clicking the login button, the test asserts that the URL is the dashboard URL and that the welcome message contains the username from the fixture. This approach keeps test data separate from test code, making tests easier to maintain and more secure.

Common Mistakes - 3 Pitfalls

Hardcoding username and password directly in the test code

Using CSS selectors that are brittle or too generic instead of stable IDs

Not waiting for the fixture to load before using its data

Bonus Challenge

Now add data-driven testing with 3 different user credentials stored in the JSON fixture file.

Show Hint

Practice

1. What is the main purpose of using JSON fixture files in Cypress tests?

easy

A. To store test data separately from test code for easy reuse

B. To write test assertions directly inside the JSON file

C. To configure Cypress plugins and environment variables

D. To define custom commands for Cypress tests

Solution

1. Step 1: Understand fixture file role

   Fixture files hold static data like user info or responses to use in tests.

2. Step 2: Identify purpose in Cypress

   They separate test data from code, making tests cleaner and reusable.

3. Final Answer:

   To store test data separately from test code for easy reuse -> Option A

4. Quick Check:

   Fixture files = test data storage [OK]

Hint: Fixtures hold test data, not code or configs [OK]

Common Mistakes:

• Thinking fixtures contain test logic
• Confusing fixtures with config files
• Using fixtures to write assertions

2. Which of the following is the correct way to load a JSON fixture file named user.json in a Cypress test?

easy

A. cy.getFixture('user.json').then((data) => { /* use data */ })

B. cy.loadFixture('user.json').then((data) => { /* use data */ })

C. cy.fixture('user.json').then((data) => { /* use data */ })

D. cy.readFile('user.json').then((data) => { /* use data */ })

Solution

1. Step 1: Recall Cypress fixture command

   Cypress uses cy.fixture() to load fixture files from the fixtures folder.

2. Step 2: Check method names

   Only cy.fixture() is the correct Cypress command; others do not exist or are incorrect.

3. Final Answer:

   cy.fixture('user.json').then((data) => { /* use data */ }) -> Option C

4. Quick Check:

   Use cy.fixture() to load JSON files [OK]

Hint: Use cy.fixture() to load JSON files in Cypress [OK]

Common Mistakes:

• Using non-existent commands like cy.loadFixture
• Confusing cy.readFile with cy.fixture
• Omitting the .then() to access data

3. Given the fixture file user.json with content:

{"name": "Alice", "age": 30}

What will the following Cypress code print to the console?

cy.fixture('user.json').then((user) => {
  console.log(user.name);
  console.log(user.age + 5);
})

medium

A. "user" and 35

B. "Alice" and 35

C. "Alice" and "35"

D. undefined and NaN

Solution

1. Step 1: Understand fixture data structure

   The JSON has keys "name" with value "Alice" and "age" with value 30 (number).

2. Step 2: Analyze console.log statements

   First logs user.name which is "Alice". Second logs user.age + 5, which is 30 + 5 = 35.

3. Final Answer:

   "Alice" and 35 -> Option B

4. Quick Check:

   Access JSON keys correctly = "Alice" and 35 [OK]

Hint: JSON values keep their types; numbers add normally [OK]

Common Mistakes:

• Treating numbers as strings and concatenating
• Using wrong keys or misspelling
• Expecting undefined from valid fixture keys

4. You wrote this Cypress test code to load a fixture:

cy.fixture('config.json').then((config) => {
  expect(config.timeout).to.equal(5000)
})

But the test fails with TypeError: Cannot read property 'timeout' of undefined. What is the most likely cause?

medium

A. The then callback is missing a parameter

B. The expect syntax is incorrect

C. The fixture file contains invalid JSON syntax

D. The fixture file config.json does not exist or is misnamed

Solution

1. Step 1: Analyze error message

   The error says config is undefined, so config.timeout fails.

2. Step 2: Check fixture loading causes

   If the fixture file is missing or misnamed, cy.fixture() returns undefined, causing this error.

3. Final Answer:

   The fixture file config.json does not exist or is misnamed -> Option D

4. Quick Check:

   Missing fixture file = undefined data [OK]

Hint: Check fixture file name and location first [OK]

Common Mistakes:

• Assuming expect syntax causes undefined error
• Ignoring fixture file path or name typos
• Not validating JSON file existence

5. You have a fixture file users.json containing an array of user objects:

[{"id":1,"name":"Bob"},{"id":2,"name":"Carol"},{"id":3,"name":"Dave"}]

How can you write a Cypress test to check that the user with id 2 has the name "Carol"?

hard

A. cy.fixture('users.json').then(users => { expect(users.find(u => u.id === 2).name).to.equal('Carol') })

B. cy.fixture('users.json').then(users => { expect(users[2].name).to.equal('Carol') })

C. cy.fixture('users.json').then(users => { expect(users.id === 2).to.equal('Carol') })

D. cy.fixture('users.json').then(users => { expect(users.name).to.include('Carol') })

Solution

1. Step 1: Understand fixture data structure

   The fixture is an array of objects, each with id and name.

2. Step 2: Find user with id 2 and check name

   Use find() to get the user object where id === 2, then check its name.

3. Final Answer:

   cy.fixture('users.json').then(users => { expect(users.find(u => u.id === 2).name).to.equal('Carol') }) -> Option A

4. Quick Check:

   Use find() to locate object by id [OK]

Hint: Use array.find() to locate object by property [OK]

Common Mistakes:

• Using wrong array index instead of find()
• Comparing id directly to name
• Accessing properties on the whole array