Why custom commands reduce duplication in Cypress - Test Execution Impact

Test Overview

This test demonstrates how using a custom Cypress command reduces code duplication by reusing a login process in multiple tests. It verifies that the user can successfully log in using the custom command.

Test Code - Cypress

Cypress

// cypress/support/commands.js
Cypress.Commands.add('login', (username, password) => {
  cy.get('#username').type(username)
  cy.get('#password').type(password)
  cy.get('#login-button').click()
})

// cypress/e2e/login_spec.cy.js
describe('Login Tests with Custom Command', () => {
  beforeEach(() => {
    cy.visit('/login')
  })

  it('logs in successfully using custom command', () => {
    cy.login('user1', 'pass123')
    cy.url().should('include', '/dashboard')
    cy.get('h1').should('contain', 'Welcome')
  })

  it('logs in another user using custom command', () => {
    cy.login('user2', 'pass456')
    cy.url().should('include', '/dashboard')
    cy.get('h1').should('contain', 'Welcome')
  })
})

Execution Trace - 9 Steps

Step	Action	System State	Assertion	Result
1	Test starts and browser opens	Browser is ready to run tests	—	PASS
2	Navigates to /login page	Login page is displayed with username, password fields and login button	URL includes '/login'	PASS
3	Calls custom command cy.login('user1', 'pass123')	Username and password fields are filled, login button is clicked	—	PASS
4	Checks URL includes '/dashboard' after login	Dashboard page is loaded	URL contains '/dashboard'	PASS
5	Checks page header contains 'Welcome'	Dashboard page shows welcome message	Header text contains 'Welcome'	PASS
6	Starts second test, navigates to /login page	Login page is displayed again	URL includes '/login'	PASS
7	Calls custom command cy.login('user2', 'pass456')	Username and password fields are filled with new user, login button clicked	—	PASS
8	Checks URL includes '/dashboard' after second login	Dashboard page is loaded for second user	URL contains '/dashboard'	PASS
9	Checks page header contains 'Welcome' for second user	Dashboard page shows welcome message	Header text contains 'Welcome'	PASS

Failure Scenario

Failing Condition: If the custom command cy.login fails to find username or password fields or login button

Execution Trace Quiz - 3 Questions

What is the main benefit of using the custom command cy.login in these tests?

A It changes the URL automatically

B It makes the test run faster by skipping login

C It reduces code duplication by reusing login steps

D It disables assertions in the test

Key Result

Using custom commands in Cypress helps keep tests clean and avoids repeating the same steps, making tests easier to maintain and read.

Practice

1. Why do custom commands in Cypress help reduce duplication in test code?

easy

A. They replace the need for assertions in tests.

B. They automatically find bugs in your code.

C. They let you write common actions once and reuse them in many tests.

D. They make tests run faster by skipping steps.

Solution

1. Step 1: Understand what duplication means in tests

   Duplication means writing the same code multiple times, which makes tests harder to maintain.

2. Step 2: Role of custom commands in Cypress

   Custom commands let you write a common action once, like logging in, and reuse it everywhere, reducing repeated code.

3. Final Answer:

   They let you write common actions once and reuse them in many tests. -> Option C

4. Quick Check:

   Reuse common actions = less duplication [OK]

Hint: Custom commands = write once, use many times [OK]

Common Mistakes:

• Thinking custom commands speed up test execution
• Believing custom commands remove the need for assertions
• Assuming custom commands automatically fix bugs

2. Which of the following is the correct way to define a custom command in Cypress?

easy

A. cy.addCommand('login', () => { cy.visit('/login') })

B. cy.Commands.create('login', () => { cy.visit('/login') })

C. Cypress.createCommand('login', () => { cy.visit('/login') })

D. Cypress.Commands.add('login', () => { cy.visit('/login') })

Solution

1. Step 1: Recall Cypress syntax for custom commands

   The correct method to add a custom command is Cypress.Commands.add.

2. Step 2: Check each option's syntax

   Only Cypress.Commands.add('login', () => { cy.visit('/login') }) uses Cypress.Commands.add correctly with the command name and function.

3. Final Answer:

   Cypress.Commands.add('login', () => { cy.visit('/login') }) -> Option D

4. Quick Check:

   Correct method is Cypress.Commands.add [OK]

Hint: Custom commands use Cypress.Commands.add() [OK]

Common Mistakes:

• Using cy.Commands instead of Cypress.Commands
• Using createCommand or addCommand which don't exist
• Mixing up method names and object names

3. Given this custom command definition:

 Cypress.Commands.add('login', (user) => { cy.get('#username').type(user.name); cy.get('#password').type(user.pass); cy.get('#submit').click(); }); 

What will happen when you run this test code?

 cy.login({name: 'alice', pass: '1234'}); cy.url().should('include', '/dashboard'); 

medium

A. The test types username and password, clicks submit, then checks URL includes '/dashboard'.

B. The test will fail because custom commands cannot take arguments.

C. The test will skip typing password and only type username.

D. The test will throw a syntax error due to missing return statement.

Solution

1. Step 1: Understand the custom command behavior

   The 'login' command types the username and password from the passed object and clicks submit.

2. Step 2: Analyze the test code execution

   Calling cy.login with user data runs the command, then the test asserts the URL includes '/dashboard'.

3. Final Answer:

   The test types username and password, clicks submit, then checks URL includes '/dashboard'. -> Option A

4. Quick Check:

   Custom command with args runs actions then assertion passes [OK]

Hint: Custom commands can take arguments and run steps [OK]

Common Mistakes:

• Thinking custom commands can't accept parameters
• Assuming missing return causes syntax error
• Believing some steps are skipped automatically

4. You wrote this custom command:

 Cypress.Commands.add('clickButton', () => { cy.get('button.submit').click(); }); 

But your tests fail with "Cannot read property 'click' of undefined". What is the likely problem?

medium

A. You forgot to call cy.visit() before using the command.

B. The selector 'button.submit' does not match any element on the page.

C. Custom commands cannot use cy.get inside them.

D. The command name 'clickButton' is reserved and cannot be used.

Solution

1. Step 1: Understand the error message

   "Cannot read property 'click' of undefined" means cy.get did not find the element, so it returned undefined.

2. Step 2: Check possible causes

   If the selector does not match any element, cy.get returns nothing, causing the error when calling click.

3. Final Answer:

   The selector 'button.submit' does not match any element on the page. -> Option B

4. Quick Check:

   Selector missing element = click fails [OK]

Hint: Check if selector matches elements before clicking [OK]

Common Mistakes:

• Assuming cy.get can't be used in custom commands
• Forgetting to visit the page (may cause no elements)
• Thinking command names are reserved keywords

5. You want to create a custom command fillForm that fills multiple fields on a page. Which approach best reduces duplication and improves test readability?

hard

A. Create fillForm to accept an object with field names and values, then fill each field inside the command.

B. Write separate commands for each field and call them one by one in tests.

C. Copy and paste the same cy.get().type() lines in every test needing the form filled.

D. Use cy.exec() to run external scripts that fill the form.

Solution

1. Step 1: Consider duplication and readability

   Copy-pasting code (Copy and paste the same cy.get().type() lines in every test needing the form filled.) causes duplication and harder maintenance.

2. Step 2: Evaluate options for custom commands

   Creating one command that accepts an object and fills all fields (Create fillForm to accept an object with field names and values, then fill each field inside the command.) centralizes logic and improves readability.

3. Step 3: Analyze other options

   Separate commands (Write separate commands for each field and call them one by one in tests.) increase calls and complexity; cy.exec (Use cy.exec() to run external scripts that fill the form.) is not for UI actions.

4. Final Answer:

   Create fillForm to accept an object with field names and values, then fill each field inside the command. -> Option A

5. Quick Check:

   One command with params reduces duplication best [OK]

Hint: Use one paramized command for multiple fields [OK]

Common Mistakes:

• Writing many small commands instead of one flexible one
• Copy-pasting code in tests instead of reusing commands
• Using cy.exec for UI interactions