Why plugins extend Cypress capabilities - Test Execution Impact

Test Overview

This test checks that a Cypress custom command correctly extends Cypress commands by adding a custom command. It verifies the custom command runs and produces the expected result.

Test Code - Cypress

Cypress

/// <reference types="cypress" />

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

// cypress/integration/login_spec.js
describe('Login with custom command', () => {
  it('should login successfully using the custom login command', () => {
    cy.visit('https://example.cypress.io/login')
    cy.login('user1', 'password123')
    cy.url().should('include', '/dashboard')
    cy.get('h1').should('contain.text', 'Dashboard')
  })
})

Execution Trace - 6 Steps

Step	Action	System State	Assertion	Result
1	Test starts	Cypress test runner initialized	—	PASS
2	Browser opens and navigates to 'https://example.cypress.io/login'	Login page with username, password fields and login button is visible	—	PASS
3	Custom command 'login' is called with username 'user1' and password 'password123'	Username and password fields are filled, login button is clicked	—	PASS
4	Test waits for navigation to '/dashboard' page	Dashboard page loads with heading 'Dashboard'	URL includes '/dashboard'	PASS
5	Check that the page heading contains text 'Dashboard'	Heading element visible with correct text	Heading text contains 'Dashboard'	PASS
6	Test ends successfully	Test passed, no errors	—	PASS

Failure Scenario

Failing Condition: Custom command 'login' is not registered or fails to fill fields and click login

Execution Trace Quiz - 3 Questions

What does the custom Cypress command 'login' do in this test?

A Fills username and password fields and clicks login button

B Navigates directly to the dashboard page

C Checks if the login button is visible

D Reloads the login page

Key Result

Using custom commands in Cypress helps reuse code and extend testing capabilities, making tests simpler and easier to maintain.

Practice

1. What is the main reason to use plugins in Cypress?

easy

A. To add extra features that work outside the browser

B. To write test cases faster inside the browser

C. To change the browser's user interface

D. To automatically fix test failures

Solution

1. Step 1: Understand Cypress plugin purpose

   Plugins let Cypress do things that normal browser tests cannot, like file system access or custom tasks.

2. Step 2: Compare options with plugin use

   Only To add extra features that work outside the browser correctly describes extending Cypress outside the browser environment.

3. Final Answer:

   To add extra features that work outside the browser -> Option A

4. Quick Check:

   Plugins extend Cypress beyond browser limits = C [OK]

Hint: Plugins add power outside browser, not inside tests [OK]

Common Mistakes:

• Thinking plugins only speed up test writing
• Confusing plugins with UI changes
• Believing plugins fix test failures automatically

2. Which file is used to write Cypress plugins?

easy

A. cypress/support/commands.js

B. cypress/plugins/index.js

C. cypress/integration/spec.js

D. cypress.json

Solution

1. Step 1: Identify plugin file location

   Cypress plugins are written in the cypress/plugins/index.js file as per Cypress structure.

2. Step 2: Eliminate other files

   Other files are for commands, tests, or config, not plugins.

3. Final Answer:

   cypress/plugins/index.js -> Option B

4. Quick Check:

   Plugins live in plugins/index.js file = A [OK]

Hint: Plugins always go in plugins/index.js file [OK]

Common Mistakes:

• Choosing support or integration files for plugins
• Confusing config file with plugin file
• Not knowing Cypress folder structure

3. What will this plugin code do?

module.exports = (on, config) => {
  on('task', {
    log(message) {
      console.log(message)
      return null
    }
  })
}

medium

A. Creates a new browser event listener

B. Runs a test inside the browser console

C. Defines a task named 'log' that prints messages to the console

D. Overrides Cypress default logging behavior

Solution

1. Step 1: Analyze the plugin code

   The code uses on('task', {...}) to define a custom task named 'log' that prints a message to the Node console.

2. Step 2: Understand task purpose

   This task can be called from tests to log messages outside the browser.

3. Final Answer:

   Defines a task named 'log' that prints messages to the console -> Option C

4. Quick Check:

   Task 'log' prints messages = D [OK]

Hint: Tasks run in Node, not browser console [OK]

Common Mistakes:

• Thinking task runs inside browser
• Confusing task with event listener
• Assuming it overrides default logs

4. Identify the error in this plugin code:

module.exports = (on, config) => {
  on('task', {
    readFile(path) {
      return fs.readFileSync(path, 'utf8')
    }
  })
}

medium

A. Missing import of 'fs' module

B. Wrong event name instead of 'task'

C. Incorrect return type for readFile

D. Plugin file should be JSON, not JS

Solution

1. Step 1: Check code dependencies

   The code uses fs.readFileSync but does not import the 'fs' module, causing a runtime error.

2. Step 2: Verify other parts

   The event name 'task' is correct, return type is valid, and plugin files are JavaScript files.

3. Final Answer:

   Missing import of 'fs' module -> Option A

4. Quick Check:

   Using fs without import causes error = B [OK]

Hint: Always import Node modules before use in plugins [OK]

Common Mistakes:

• Assuming event name is wrong
• Thinking return type must be a promise
• Believing plugin files must be JSON

5. You want to create a plugin that reads a JSON file and returns its content as an object to your test. Which plugin code correctly does this?

const fs = require('fs')

module.exports = (on, config) => {
  on('task', {
    readJson(path) {
      const content = fs.readFileSync(path, 'utf8')
      return JSON.parse(content)
    }
  })
}

hard

A. This code needs to use asynchronous fs.readFile instead

B. This code will fail because JSON.parse cannot be used in plugins

C. This code should return content without parsing

D. This code correctly reads and parses JSON file content

Solution

1. Step 1: Check file reading method

   The code uses fs.readFileSync to read the file synchronously, which is valid in plugins.

2. Step 2: Verify JSON parsing

   It correctly parses the JSON string to an object using JSON.parse and returns it.

3. Final Answer:

   This code correctly reads and parses JSON file content -> Option D

4. Quick Check:

   Sync read + JSON.parse returns object = A [OK]

Hint: Use sync read and JSON.parse in plugins for JSON files [OK]

Common Mistakes:

• Thinking JSON.parse is disallowed in plugins
• Believing async read is required
• Returning raw string instead of parsed object