Why custom commands reduce duplication in Cypress - The Real Reasons

The Big Idea

What if you could fix one line and update hundreds of tests instantly?

The Scenario

Imagine testing a website where you must log in before every test. You write the same steps to enter username, password, and click login in every test file.

The Problem

Typing the same login steps repeatedly wastes time and makes your tests hard to update. If the login process changes, you must fix every test manually, risking mistakes and delays.

The Solution

Custom commands let you write the login steps once and reuse them everywhere. This keeps your tests clean, easy to read, and simple to update if the login changes.

Before vs After

✗ Before

cy.get('#user').type('name')
cy.get('#pass').type('secret')
cy.get('#login').click()

✓ After

cy.login('name', 'secret')

What It Enables

Custom commands unlock faster test writing and easier maintenance by removing repeated code.

Real Life Example

A team testing an online store uses a custom command for login. When the login page updates, they change the command once, and all tests keep working smoothly.

Key Takeaways

Manual repetition slows testing and causes errors.

Custom commands bundle repeated steps into one reusable action.

This saves time and makes tests easier to update and understand.

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