Why Preserving state between tests in Cypress? - Purpose & Use Cases

The Big Idea

What if you never had to log in again for every single test you write?

The Scenario

Imagine testing a website where you must log in before each test. You open the site, enter your username and password every single time manually or write repetitive steps in your test scripts.

The Problem

This manual or repetitive approach is slow and boring. It wastes time and can cause mistakes if you forget a step or mistype credentials. It also makes tests fragile and hard to maintain.

The Solution

Preserving state between tests means saving things like login info once and reusing it automatically. This way, tests run faster and more reliably without repeating the same setup again and again.

Before vs After

✗ Before

beforeEach(() => {
  cy.visit('/login');
  cy.get('#user').type('user');
  cy.get('#pass').type('pass');
  cy.get('#submit').click();
});

✓ After

before(() => {
  cy.login('user', 'pass');
});

beforeEach(() => {
  cy.restoreSession();
});

What It Enables

It enables running many tests quickly and smoothly without repeating boring setup steps, making testing more efficient and fun.

Real Life Example

Think of testing an online store where you log in once, then check your cart, order history, and profile in separate tests without logging in each time.

Key Takeaways

Manual repeated setup wastes time and causes errors.

Preserving state saves login or session info once for all tests.

This makes tests faster, simpler, and easier to maintain.

Practice

1. What is the main reason to preserve state between tests in Cypress?

easy

A. To clear all cookies after each test

B. To make tests dependent on each other

C. To avoid repeating login steps and speed up test execution

D. To disable assertions in tests

Solution

1. Step 1: Understand test state preservation

   Preserving state means keeping some data like cookies so tests don't repeat setup steps.

2. Step 2: Identify the benefit

   Keeping state avoids repeating login or setup, making tests faster and more efficient.

3. Final Answer:

   To avoid repeating login steps and speed up test execution -> Option C

4. Quick Check:

   Preserving state = faster tests [OK]

Hint: Preserve state to skip repeated steps and save time [OK]

Common Mistakes:

• Thinking tests should be dependent on each other
• Believing preserving state clears cookies
• Assuming preserving state disables assertions

2. Which of the following is the correct syntax to preserve a cookie named 'session_id' only once in Cypress?

easy

A. Cypress.Cookies.preserveOnce('session_id')

B. cy.preserveCookie('session_id')

C. Cypress.preserveCookieOnce('session_id')

D. cy.Cookies.preserve('session_id')

Solution

1. Step 1: Recall Cypress cookie preservation method

   The correct method to preserve cookies once is Cypress.Cookies.preserveOnce.

2. Step 2: Match method and argument

   The method takes the cookie name as a string argument, e.g., 'session_id'.

3. Final Answer:

   Cypress.Cookies.preserveOnce('session_id') -> Option A

4. Quick Check:

   Preserve once = Cypress.Cookies.preserveOnce [OK]

Hint: Use Cypress.Cookies.preserveOnce('cookieName') to keep cookies once [OK]

Common Mistakes:

• Using cy.preserveCookie which does not exist
• Mixing method names like preserveCookieOnce
• Calling preserve on cy.Cookies which is invalid

3. Given the following Cypress test code, what will be the output of the second test?

describe('Test Suite', () => {
  beforeEach(() => {
    Cypress.Cookies.preserveOnce('token')
  })

  it('Test 1: Set cookie', () => {
    cy.setCookie('token', 'abc123')
  })

  it('Test 2: Check cookie', () => {
    cy.getCookie('token').should('have.property', 'value', 'abc123')
  })
})

medium

A. Test 2 passes because the 'token' cookie is preserved

B. Test 2 fails because cookies are cleared between tests

C. Test 2 throws a syntax error

D. Test 2 passes but the cookie value is empty

Solution

1. Step 1: Analyze cookie preservation in beforeEach

   The beforeEach hook preserves the 'token' cookie between tests using Cypress.Cookies.preserveOnce('token').

2. Step 2: Understand cookie setting and checking

   Test 1 sets the cookie 'token' to 'abc123'. Test 2 checks the cookie value. Since the cookie is preserved, the check passes.

3. Final Answer:

   Test 2 fails because cookies are cleared between tests -> Option B

4. Quick Check:

   PreserveOnce keeps cookie for next test [OK]

Hint: Preserve cookie in beforeEach to keep it for next test [OK]

Common Mistakes:

• Assuming cookies clear automatically between tests
• Thinking preserveOnce clears cookies
• Confusing syntax causing errors

4. You wrote this code to preserve cookies but the second test fails because the cookie is missing:

beforeEach(() => {
  Cypress.Cookies.preserveOnce('auth_token')
})

it('Login test', () => {
  cy.setCookie('auth_token', 'xyz789')
})

it('Dashboard test', () => {
  cy.getCookie('auth_token').should('exist')
})

What is the likely cause of the failure?

medium

A. The cookie is set after the beforeEach hook runs, so it is not preserved

B. The cookie name is misspelled in preserveOnce

C. Cypress cannot preserve cookies between tests

D. The assertion syntax is incorrect

Solution

1. Step 1: Understand when preserveOnce runs

   The beforeEach hook runs before each test, so it preserves cookies existing before the test starts.

2. Step 2: Analyze cookie setting timing

   The cookie is set inside the first test, after beforeEach runs, so it is not preserved for the next test.

3. Final Answer:

   The cookie is set after the beforeEach hook runs, so it is not preserved -> Option A

4. Quick Check:

   PreserveOnce must run after cookie set [OK]

Hint: Set cookies before preserveOnce runs to keep them [OK]

Common Mistakes:

• Thinking preserveOnce preserves cookies set during the test
• Assuming Cypress can't preserve cookies
• Blaming assertion syntax instead of timing

5. You want to preserve multiple cookies named 'token' and 'user_id' across all tests without calling preserveOnce in every test. Which is the best way to do this in Cypress?

hard

A. Disable cookie clearing globally with Cypress.config

B. Call Cypress.Cookies.preserveOnce('token', 'user_id') in each test

C. Set cookies again in every test manually

D. Use Cypress.Cookies.defaults({ whitelist: ['token', 'user_id'] }) in support file

Solution

1. Step 1: Understand preserving multiple cookies globally

   Using Cypress.Cookies.defaults with a preserve array keeps specified cookies across all tests automatically.

2. Step 2: Compare with other options

   Calling preserveOnce in every test is repetitive. Manually setting cookies each time is inefficient. Disabling cookie clearing globally is not recommended.

3. Final Answer:

   Use Cypress.Cookies.defaults({ whitelist: ['token', 'user_id'] }) in support file -> Option D

4. Quick Check:

   Defaults preserve multiple cookies globally [OK]

Hint: Use Cypress.Cookies.defaults to preserve cookies globally [OK]

Common Mistakes:

• Calling preserveOnce repeatedly instead of defaults
• Manually resetting cookies each test
• Trying to disable cookie clearing globally