Test isolation strategies in Cypress - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Why is test isolation important in Cypress?

In Cypress testing, why do we need to isolate tests from each other?

A To prevent Cypress from opening multiple browser windows

B To make tests run slower and use more resources

C To allow tests to share data and speed up execution

D To ensure tests do not depend on each other's state and results are reliable

💡 Hint

Think about what happens if one test changes something that affects another test.

Test isolation ensures each test runs independently without side effects from others, making results consistent and trustworthy.

❓ Predict Output

intermediate

What is the output of this Cypress test suite?

Consider this Cypress test code. What will be the value of count after all tests run?

Cypress

let count = 0;
describe('Counter tests', () => {
  beforeEach(() => {
    count = 0;
  });
  it('increments count', () => {
    count += 1;
    expect(count).to.equal(1);
  });
  it('increments count again', () => {
    count += 1;
    expect(count).to.equal(1);
  });
});

// What is the final value of count?

A 2

B 0

C 1

D Undefined

💡 Hint

Look at what beforeEach does before each test.

The beforeEach resets count to 0 before each test. Each test increments it to 1. After all tests, count remains 1.

❓ assertion

advanced

Which assertion best verifies test isolation of localStorage?

You want to confirm that localStorage is cleared between tests in Cypress. Which assertion correctly checks this?

A expect(localStorage.getItem('token')).to.equal('token');

B expect(localStorage.getItem('token')).to.be.null;

C expect(localStorage.length).to.be.greaterThan(0);

D expect(localStorage.token).to.equal('');

💡 Hint

Think about what value localStorage returns when a key does not exist.

If localStorage is cleared, getItem returns null for any key. Checking for null confirms isolation.

🔧 Debug

advanced

Identify the test isolation issue in this Cypress code

Look at this Cypress test code. What causes the tests to fail intermittently due to poor isolation?

Cypress

let sharedData = [];
describe('Shared data tests', () => {
  it('adds item', () => {
    sharedData.push('item1');
    expect(sharedData).to.include('item1');
  });
  it('checks empty array', () => {
    expect(sharedData).to.be.empty;
  });
});

A sharedData is not reset between tests, causing state leakage

B The expect syntax is incorrect and causes errors

C Cypress does not support arrays in tests

D Tests run in parallel causing race conditions

💡 Hint

Check if sharedData is cleared before each test.

sharedData is declared outside tests and not reset, so the second test sees data from the first, breaking isolation.

❓ framework

expert

Which Cypress command best ensures test isolation by resetting application state?

In Cypress, which command is best used to reset the application state between tests to ensure isolation?

A cy.visit('/')

B cy.resetAppState()

C cy.reload()

D cy.clearCookies()

💡 Hint

Think about how to start fresh with a clean page load.

cy.visit('/') reloads the app from the start URL, resetting state including cookies, localStorage, and UI.

Practice

1. What is the main purpose of test isolation in Cypress testing?

easy

A. To speed up test execution by running all tests together

B. To share data between tests for faster setup

C. To keep tests independent and avoid interference between them

D. To reduce the number of tests needed

Solution

1. Step 1: Understand test isolation concept

   Test isolation means each test runs independently without relying on others.

2. Step 2: Identify the main benefit

   This independence avoids interference and makes tests reliable and easier to debug.

3. Final Answer:

   To keep tests independent and avoid interference between them -> Option C

4. Quick Check:

   Test isolation = Independent tests [OK]

Hint: Test isolation means no test depends on another [OK]

Common Mistakes:

• Thinking tests should share data to run faster
• Believing test isolation reduces total tests
• Confusing isolation with parallel execution

2. Which Cypress hook is best used to reset application state before each test to ensure isolation?

easy

A. beforeEach

B. before

C. after

D. afterEach

Solution

1. Step 1: Recall Cypress hooks purpose

   beforeEach runs before every test, ideal for resetting state.

2. Step 2: Compare with other hooks

   before runs once before all tests, after and afterEach run after tests, so they don't reset state before tests.

3. Final Answer:

   beforeEach -> Option A

4. Quick Check:

   Reset state before each test = beforeEach [OK]

Hint: Use beforeEach to reset state before every test [OK]

Common Mistakes:

• Using before which runs only once
• Confusing afterEach with beforeEach
• Not resetting state at all

3. Consider this Cypress test code snippet:

describe('My Tests', () => {
  beforeEach(() => {
    cy.visit('/login')
  })

  it('Test A', () => {
    cy.get('#username').type('user1')
    cy.get('#password').type('pass1')
    cy.get('button').click()
    cy.url().should('include', '/dashboard')
  })

  it('Test B', () => {
    cy.get('#username').type('user2')
    cy.get('#password').type('pass2')
    cy.get('button').click()
    cy.url().should('include', '/dashboard')
  })
})

What is the main benefit of using beforeEach here?

medium

A. It visits the login page once before all tests

B. It visits the login page before each test to isolate them

C. It skips the login page for Test B

D. It runs tests faster by sharing the login page

Solution

1. Step 1: Analyze beforeEach usage

   beforeEach runs before every test, so it visits the login page before Test A and Test B.

2. Step 2: Understand test isolation effect

   This ensures each test starts fresh on the login page, isolating tests and avoiding state carryover.

3. Final Answer:

   It visits the login page before each test to isolate them -> Option B

4. Quick Check:

   beforeEach = fresh start per test [OK]

Hint: beforeEach runs before every test, isolating them [OK]

Common Mistakes:

• Thinking beforeEach runs only once
• Assuming tests share the same page state
• Believing it skips steps for some tests

4. You wrote tests with beforeEach to reset state, but tests still fail due to shared data. What is the likely mistake?

medium

A. Using before instead of beforeEach

B. Not visiting the page in any hook

C. Using afterEach to reset state

D. Running tests in parallel

Solution

1. Step 1: Identify hook usage problem

   If before is used, it runs once before all tests, so state is not reset before each test.

2. Step 2: Understand impact on test isolation

   This causes shared data between tests, breaking isolation and causing failures.

3. Final Answer:

   Using before instead of beforeEach -> Option A

4. Quick Check:

   beforeEach resets state per test, before does not [OK]

Hint: Use beforeEach, not before, to reset state each test [OK]

Common Mistakes:

• Confusing before and beforeEach hooks
• Assuming afterEach resets state before tests
• Ignoring test parallelism effects

5. You want to run Cypress tests in parallel on CI to speed up testing. Which test isolation strategy helps ensure tests run reliably in parallel?

hard

A. Sharing global variables between tests

B. Running all tests in a single browser session without reset

C. Disabling test retries to avoid repeated runs

D. Using beforeEach to reset state and avoid shared data

Solution

1. Step 1: Understand parallel test challenges

   Parallel tests run simultaneously, so shared state causes flaky failures.

2. Step 2: Identify isolation strategy for parallel runs

   Using beforeEach to reset state and avoid shared data ensures each test is independent and reliable.

3. Final Answer:

   Using beforeEach to reset state and avoid shared data -> Option D

4. Quick Check:

   Parallel tests need isolated state = beforeEach [OK]

Hint: Reset state before each test for reliable parallel runs [OK]

Common Mistakes:

• Sharing global variables causing conflicts
• Running tests without resetting state
• Disabling retries instead of fixing isolation