Task command for Node operations in Cypress - Build an Automation Script

Verify reading a file content using Cypress task command

Preconditions (1)

Step 1: Open the Cypress test runner

Step 2: Run the test that calls a Cypress task to read 'sample.txt' content from Node

Step 3: Verify the content returned by the task matches 'Hello Cypress!'

✅ Expected Result: The test passes confirming the file content read via Node task matches the expected string

Automation Requirements - Cypress

Assertions Needed:

Assert the content returned from the task equals 'Hello Cypress!'

Best Practices:

Use Cypress task command to perform Node file system operations

Keep Node code in plugins or support file

Use explicit assertion with .should or expect

Avoid direct file system calls in test code

Automated Solution

Cypress

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

// cypress/plugins/index.js
const fs = require('fs');

module.exports = (on, config) => {
  on('task', {
    readFileContent(filename) {
      return new Promise((resolve, reject) => {
        fs.readFile(`cypress/fixtures/${filename}`, 'utf8', (err, data) => {
          if (err) {
            return reject(err);
          }
          resolve(data);
        });
      });
    }
  });
};

// cypress/e2e/readFileTask.cy.js

describe('Read file content using Cypress task', () => {
  it('should read sample.txt content via task', () => {
    cy.task('readFileContent', 'sample.txt').then((content) => {
      expect(content).to.equal('Hello Cypress!');
    });
  });
});

The plugins/index.js file defines a Cypress task named readFileContent that uses Node's fs.readFile to read a file asynchronously from the cypress/fixtures folder. It returns a promise that resolves with the file content.

The test file readFileTask.cy.js calls this task with cy.task('readFileContent', 'sample.txt'). The returned content is then asserted to equal the expected string 'Hello Cypress!' using expect.

This approach keeps Node operations separate from browser test code and uses Cypress best practices for asynchronous tasks and assertions.

Common Mistakes - 3 Pitfalls

Calling Node fs.readFile directly inside the test without using cy.task

Not returning a promise or value from the task function

{'mistake': 'Hardcoding file paths outside the Cypress folder structure', 'why_bad': 'This reduces test portability and can cause path resolution issues on different machines.', 'correct_approach': "Use relative paths inside the Cypress project folders like 'cypress/fixtures' for test files."}

Bonus Challenge

Now add data-driven testing to read three different files ('sample1.txt', 'sample2.txt', 'sample3.txt') and verify their contents using the same task command.

Show Hint

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