Writing to files (cy.writeFile) in Cypress - Build an Automation Script

Write user data to a JSON file using Cypress

Preconditions (2)

Step 1: Open the Cypress test runner

Step 2: Create a test that uses cy.writeFile to write a JSON object with user details (name, email) to 'cypress/fixtures/user.json'

Step 3: Run the test

Step 4: Verify that the file 'cypress/fixtures/user.json' is created or updated with the correct JSON content

✅ Expected Result: The file 'cypress/fixtures/user.json' contains the exact JSON object with the user details written by the test

Automation Requirements - Cypress

Assertions Needed:

Verify the file 'cypress/fixtures/user.json' exists after writing

Verify the file content matches the JSON object written

Best Practices:

Use cy.writeFile with a valid path relative to the project root

Use JSON.stringify or pass an object directly to cy.writeFile

Avoid hardcoding absolute paths

Use cy.readFile to verify file content

Keep test data simple and clear

Automated Solution

Cypress

describe('Write to file test', () => {
  it('writes user data to a JSON file', () => {
    const userData = {
      name: 'Alice',
      email: '[e-mail]'
    };

    // Write the userData object to a JSON file
    cy.writeFile('cypress/fixtures/user.json', userData);

    // Verify the file content matches userData
    cy.readFile('cypress/fixtures/user.json').should('deep.equal', userData);
  });
});

This test defines a simple user data object with name and email.

It uses cy.writeFile to write this object to cypress/fixtures/user.json. Passing the object directly lets Cypress handle JSON formatting.

Then, cy.readFile reads the file back and asserts that its content deeply equals the original object. This confirms the write was successful and accurate.

Using relative paths keeps the test portable. Assertions ensure the test fails if writing or reading is incorrect.

Common Mistakes - 4 Pitfalls

{'mistake': 'Using an absolute file path in cy.writeFile', 'why_bad': 'Absolute paths can break tests on different machines or environments.', 'correct_approach': "Use relative paths like 'cypress/fixtures/user.json' so the test works anywhere."}

Passing a stringified JSON instead of an object to cy.writeFile

Not verifying the file content after writing

Not waiting for cy.writeFile to complete before reading the file

Bonus Challenge

Now add data-driven testing to write three different user objects to separate JSON files

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