Task command for Node operations in Cypress - Test Execution Trace

Test Overview

This test uses Cypress task command to perform a Node.js operation that reads a file's content. It verifies that the content returned by the task matches the expected text.

Test Code - Cypress

Cypress

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

// In cypress/plugins/index.js or cypress.config.js
module.exports = (on, config) => {
  on('task', {
    readFileContent(filename) {
      const fs = require('fs')
      return fs.readFileSync(filename, 'utf8')
    }
  })
}

// In the test file
describe('Task command for Node operations', () => {
  it('reads file content using task command', () => {
    const testFile = 'cypress/fixtures/sample.txt'
    cy.task('readFileContent', testFile).then((content) => {
      expect(content).to.contain('Hello Cypress')
    })
  })
})

Execution Trace - 7 Steps

Step	Action	System State	Assertion	Result
1	Test starts	Cypress test runner initialized	—	PASS
2	Cypress opens browser and loads test page	Browser opened with Cypress test environment	—	PASS
3	Test calls cy.task('readFileContent', 'cypress/fixtures/sample.txt')	Cypress sends task request to Node process	—	PASS
4	Node process executes task: reads file content synchronously	File 'sample.txt' content read: 'Hello Cypress! This is a sample file.'	—	PASS
5	Task returns file content to Cypress test	Cypress receives file content string	—	PASS
6	Test asserts content includes 'Hello Cypress'	Content string contains expected text	expect(content).to.contain('Hello Cypress')	PASS
7	Test ends successfully	Test passed, no errors	—	PASS

Failure Scenario

Failing Condition: The file 'cypress/fixtures/sample.txt' does not exist or path is incorrect

Execution Trace Quiz - 3 Questions

What does the cy.task command do in this test?

A Clicks a button on the webpage

B Navigates to a new URL

C Runs a Node.js function to read a file and returns its content

D Types text into an input field

Key Result

Using Cypress task commands allows running Node.js code during tests, enabling operations like file reading that are not possible in the browser context.

Practice

1. What is the main purpose of the cy.task() command in Cypress?

easy

A. To run Node.js code during Cypress tests

B. To select elements on the webpage

C. To assert values in the DOM

D. To take screenshots automatically

Solution

1. Step 1: Understand the role of cy.task()

   The cy.task() command allows Cypress tests to execute Node.js code outside the browser environment.

2. Step 2: Differentiate from other commands

   Commands like selecting elements or assertions happen inside the browser, but cy.task() runs backend code for tasks like file access.

3. Final Answer:

   To run Node.js code during Cypress tests -> Option A

4. Quick Check:

   Node code execution = A [OK]

Hint: Remember: cy.task() runs backend Node code [OK]

Common Mistakes:

• Confusing cy.task() with DOM commands
• Thinking cy.task() runs in the browser
• Assuming cy.task() is for assertions

2. Which of the following is the correct way to call a task named readFile in a Cypress test?

easy

A. cy.command('readFile')

B. cy.readFile('readFile')

C. cy.task('readFile')

D. cy.nodeTask('readFile')

Solution

1. Step 1: Recall the syntax for calling tasks

   In Cypress, tasks defined in the config are called using cy.task('taskName').

2. Step 2: Verify other options

   cy.readFile is a different command for reading files in the browser context, not tasks. The others are invalid commands.

3. Final Answer:

   cy.task('readFile') -> Option C

4. Quick Check:

   Use cy.task() to call tasks [OK]

Hint: Use cy.task('name') to run tasks [OK]

Common Mistakes:

• Using cy.readFile instead of cy.task
• Trying non-existent commands like cy.nodeTask
• Passing task name without quotes

3. Given this task definition in cypress.config.js:

tasks: {
  getEnv() {
    return process.env.NODE_ENV
  }
}

What will this test print?

cy.task('getEnv').then(env => {
  cy.log(env)
})

medium

A. It throws a syntax error

B. It logs an empty string

C. It logs 'undefined'

D. It logs the current NODE_ENV value

Solution

1. Step 1: Understand the task function

   The task getEnv returns the value of process.env.NODE_ENV, which is the environment mode (like 'development' or 'production').

2. Step 2: Analyze the test code

   The test calls cy.task('getEnv') and logs the returned value, so it will print the current environment string.

3. Final Answer:

   It logs the current NODE_ENV value -> Option D

4. Quick Check:

   Task returns env string = B [OK]

Hint: Tasks return Node values; cy.task() logs them [OK]

Common Mistakes:

• Assuming task runs in browser context
• Expecting syntax errors from valid code
• Thinking environment variables are empty by default

4. What is wrong with this task definition in cypress.config.js?

tasks: {
  readFile(path) {
    const fs = require('fs')
    return fs.readFileSync(path, 'utf8')
  }
}

When called as cy.task('readFile', 'data.txt'), it throws an error.

medium

A. The task function must return a Promise or value, but readFileSync is synchronous

B. The task should be defined as an async function returning a Promise

C. Tasks cannot accept arguments

D. The require statement is not allowed inside tasks

Solution

1. Step 1: Understand task function requirements

   Cypress tasks should return a value or a Promise. Using synchronous readFileSync is allowed but can cause blocking issues.

2. Step 2: Identify best practice for async operations

   To avoid errors and improve performance, tasks reading files should be async and return a Promise, e.g., using fs.promises.readFile.

3. Step 3: Analyze the error cause

   The error likely occurs because Cypress expects a Promise for async tasks, so defining the task as async fixes it.

4. Final Answer:

   The task should be defined as an async function returning a Promise -> Option B

5. Quick Check:

   Async tasks return Promises = D [OK]

Hint: Use async functions for tasks doing file I/O [OK]

Common Mistakes:

• Thinking synchronous code always works in tasks
• Believing require is disallowed inside tasks
• Assuming tasks cannot take arguments

5. You want to create a Cypress task that reads a JSON file and returns only the keys of the top-level object. Which task definition is correct?

hard

A. async readKeys(file) {
const fs = require('fs').promises
const data = await fs.readFile(file, 'utf8')
return Object.keys(JSON.parse(data))
}

B. readKeys(file) {
const fs = require('fs')
const data = fs.readFileSync(file, 'utf8')
return JSON.parse(data).keys()
}

C. async readKeys(file) {
const fs = require('fs')
const data = await fs.readFile(file, 'utf8')
return Object.keys(data)
}

D. readKeys(file) {
const fs = require('fs')
const data = fs.readFileSync(file, 'utf8')
return Object.keys(data)
}

Solution

1. Step 1: Read file asynchronously and parse JSON

   async readKeys(file) { const fs = require('fs').promises const data = await fs.readFile(file, 'utf8') return Object.keys(JSON.parse(data)) } correctly uses fs.promises.readFile with await to read the file asynchronously, then parses JSON.

2. Step 2: Extract keys from parsed object

   It returns Object.keys() of the parsed JSON, which gives the top-level keys as required.

3. Step 3: Identify errors in other options

   readKeys(file) { const fs = require('fs') const data = fs.readFileSync(file, 'utf8') return JSON.parse(data).keys() } incorrectly calls .keys() on the parsed object (should use Object.keys()). Options C and D try to get keys from raw string data, which is incorrect.

4. Final Answer:

   async readKeys(file) { const fs = require('fs').promises const data = await fs.readFile(file, 'utf8') return Object.keys(JSON.parse(data)) } -> Option A

5. Quick Check:

   Async read + JSON parse + Object.keys = A [OK]

Hint: Parse JSON first, then get keys with Object.keys() [OK]

Common Mistakes:

• Calling .keys() on object instead of Object.keys()
• Trying to get keys from raw string data
• Using synchronous read without async/await properly