Test isolation strategies in Cypress - Build an Automation Script

Verify that each test runs independently with proper isolation

Preconditions (2)

Step 1: Open the application home page

Step 2: Verify that the counter value is 0

Step 3: Click the increment button once

Step 4: Verify that the counter value is 1

Step 5: Reload the page

Step 6: Verify that the counter value is reset to 0

Step 7: Run a second test that opens the home page

Step 8: Verify that the counter value is 0 without any clicks

✅ Expected Result: Each test runs independently without sharing state. The counter resets to 0 at the start of each test.

Automation Requirements - Cypress

Assertions Needed:

Verify counter value is 0 at test start

Verify counter increments correctly

Verify counter resets after page reload

Verify no state is shared between tests

Best Practices:

Use beforeEach hook to visit the page fresh for each test

Avoid sharing variables or state between tests

Use Cypress commands and assertions consistently

Use clear and maintainable selectors (data-cy attributes)

Automated Solution

Cypress

describe('Test isolation strategies', () => {
  beforeEach(() => {
    cy.visit('http://localhost:3000')
  })

  it('increments counter and verifies reset on reload', () => {
    cy.get('[data-cy=counter]').should('have.text', '0')
    cy.get('[data-cy=increment-btn]').click()
    cy.get('[data-cy=counter]').should('have.text', '1')
    cy.reload()
    cy.get('[data-cy=counter]').should('have.text', '0')
  })

  it('starts with counter at 0 without clicks', () => {
    cy.get('[data-cy=counter]').should('have.text', '0')
  })
})

The beforeEach hook visits the application fresh before each test to ensure no shared state.

The first test clicks the increment button and verifies the counter increments, then reloads the page and verifies the counter resets to 0.

The second test verifies the counter starts at 0 without any clicks, proving tests are isolated.

Selectors use data-cy attributes for stability and clarity.

Common Mistakes - 3 Pitfalls

Not using beforeEach to visit the page fresh

Sharing variables or DOM references between tests

Using brittle selectors like classes or ids that may change

Bonus Challenge

Now add a third test that clicks the increment button twice and verifies the counter shows 2, ensuring isolation from previous tests.

Show Hint

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