Reading file contents in Cypress - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of reading a JSON file with Cypress?

Given the following Cypress test code that reads a JSON file and logs a property, what will be printed in the test runner console?

Cypress

cy.readFile('cypress/fixtures/user.json').then((user) => {
  cy.log(user.name)
})

// Assume user.json content: {"name": "Alice", "age": 30}

A {name: "Alice", age: 30}

B user.name

C undefined

D Alice

💡 Hint

cy.readFile reads the file and parses JSON automatically.

cy.readFile reads the JSON file and returns the parsed object. Accessing user.name gives the string 'Alice'.

❓ assertion

intermediate

Which assertion correctly verifies file content in Cypress?

You want to check that the file 'data.txt' contains the exact text 'Hello World'. Which assertion is correct?

Cypress

cy.readFile('data.txt').should( /* assertion here */ )

A have.text('Hello World')

B contain('Hello World')

C equal('Hello World')

D include.text('Hello World')

💡 Hint

Use the assertion that checks exact equality of strings.

The 'equal' assertion checks that the file content exactly matches 'Hello World'. 'contain' checks substring, others are invalid for strings.

🔧 Debug

advanced

Why does this Cypress test fail to read the file?

Consider this test code: cy.readFile('nonexistent.json').then((data) => { cy.log(data.value) }) Why does this test fail?

Cypress

cy.readFile('nonexistent.json').then((data) => {
  cy.log(data.value)
})

A The file 'nonexistent.json' does not exist, causing an error.

B cy.log cannot log properties of objects.

C The file path is relative to the wrong folder.

D The .then callback is missing a return statement.

💡 Hint

Check if the file path is correct and file exists.

cy.readFile throws an error if the file does not exist. The test fails because 'nonexistent.json' is missing.

❓ framework

advanced

How to read a file and assert JSON property asynchronously in Cypress?

Which code snippet correctly reads 'config.json' and asserts that the 'enabled' property is true?

A cy.readFile('config.json').should('have.property', 'enabled', true)

B cy.readFile('config.json').then((config) => { expect(config.enabled).to.be.true })

C cy.readFile('config.json').should((config) => { expect(config.enabled).to.be.true })

D cy.readFile('config.json').then((config) => { assert(config.enabled === true) })

💡 Hint

Use Cypress built-in assertions for properties.

Option A uses 'should' with property check, which is the Cypress recommended way for assertions on file content.

🧠 Conceptual

expert

What is the best practice for reading large files in Cypress tests?

When reading a very large file in Cypress tests, what is the best approach to avoid slowing down tests or causing memory issues?

A Avoid reading files; instead, mock file content with fixtures.

B Split the file into smaller chunks outside Cypress and read only needed parts during tests.

C Use cy.readFile with encoding 'utf16' to reduce memory usage.

D Read the entire file with cy.readFile and process it all at once.

💡 Hint

Think about test speed and memory when handling large data.

Reading large files fully can slow tests and use much memory. Splitting files and reading only needed parts is best practice.

Practice

1. What is the primary purpose of cy.readFile() in Cypress testing?

easy

A. To read the contents of a file during a test

B. To write data to a file during a test

C. To delete a file before running tests

D. To upload a file to the server

Solution

1. Step 1: Understand the function name

   cy.readFile() suggests reading a file, not writing or deleting.

2. Step 2: Recall Cypress documentation

   This command reads file contents so tests can verify data inside files.

3. Final Answer:

   To read the contents of a file during a test -> Option A

4. Quick Check:

   cy.readFile() reads file contents [OK]

Hint: Remember: readFile reads, writeFile writes [OK]

Common Mistakes:

• Confusing readFile with writeFile
• Thinking it uploads files
• Assuming it deletes files

2. Which of the following is the correct syntax to read a JSON file named data.json using Cypress?

easy

A. cy.readFile('data.json', 'utf8')

B. cy.readFile('data.json').then((content) => { /* use content */ })

C. cy.readFile('data.json').catch((content) => { /* use content */ })

D. cy.readFile('data.json').write((content) => { /* use content */ })

Solution

1. Step 1: Identify correct method chaining

   Using then() after cy.readFile() is correct to access file content.

2. Step 2: Check other options

   catch() is for errors, not normal reading; write() is invalid here; passing 'utf8' alone is incomplete.

3. Final Answer:

   cy.readFile('data.json').then((content) => { /* use content */ }) -> Option B

4. Quick Check:

   Use then() to handle readFile content [OK]

Hint: Use then() to access file content after readFile [OK]

Common Mistakes:

• Using catch() instead of then()
• Trying to write after readFile
• Passing encoding without then()

3. Given the code below, what will be logged to the console if example.txt contains the text "Hello Cypress"?

cy.readFile('example.txt').then((text) => {
  console.log(text);
});

medium

A. Empty string

B. undefined

C. An error because readFile needs JSON

D. "Hello Cypress"

Solution

1. Step 1: Understand readFile behavior

   cy.readFile() reads file content as text by default if file is plain text.

2. Step 2: Check the file content

   The file contains "Hello Cypress", so the callback receives this string and logs it.

3. Final Answer:

   "Hello Cypress" -> Option D

4. Quick Check:

   readFile logs file text content [OK]

Hint: readFile returns file content as string for text files [OK]

Common Mistakes:

• Assuming readFile only works with JSON
• Expecting undefined instead of content
• Thinking it throws error for text files

4. Identify the error in the following Cypress code snippet that tries to read a file and assert its content:

cy.readFile('config.json').then((data) => {
  expect(data).to.equal('config');
});

medium

A. Incorrect file path syntax

B. Missing catch() to handle errors

C. Using to.equal() instead of to.deep.equal() for object comparison

D. readFile cannot be used with JSON files

Solution

1. Step 1: Understand data type returned by readFile

   Reading a JSON file returns an object, not a string.

2. Step 2: Check assertion method

   to.equal() checks strict equality, which fails for objects; to.deep.equal() is needed for object content comparison.

3. Final Answer:

   Using to.equal() instead of to.deep.equal() for object comparison -> Option C

4. Quick Check:

   Use deep.equal for object assertions [OK]

Hint: Use deep.equal for objects, equal for primitives [OK]

Common Mistakes:

• Using to.equal() for objects
• Ignoring error handling
• Assuming readFile can't read JSON

5. You want to verify that a text file notes.txt contains the word "important" anywhere in its content using Cypress. Which code snippet correctly performs this check?

hard

A. cy.readFile('notes.txt').then((text) => { expect(text.includes('important')).to.be.true; })

B. cy.readFile('notes.txt').should('contain', 'important')

C. cy.readFile('notes.txt').then((text) => { expect(text).to.equal('important'); })

D. cy.readFile('notes.txt').then((text) => { expect(text).to.have.property('important'); })

Solution

1. Step 1: Understand file content check

   We want to check if the word "important" is anywhere in the text, so we need to check substring presence.

2. Step 2: Evaluate options

   cy.readFile('notes.txt').then((text) => { expect(text.includes('important')).to.be.true; }) uses includes() and asserts true, which is correct. cy.readFile('notes.txt').should('contain', 'important') is invalid because should('contain') is for DOM elements, not file content. cy.readFile('notes.txt').then((text) => { expect(text).to.equal('important'); }) checks exact equality, which is wrong. cy.readFile('notes.txt').then((text) => { expect(text).to.have.property('important'); }) wrongly uses to.have.property() on a string.

3. Final Answer:

   cy.readFile('notes.txt').then((text) => { expect(text.includes('important')).to.be.true; }) -> Option A

4. Quick Check:

   Use includes() to check substring in file text [OK]

Hint: Use includes() inside then() to check text content [OK]

Common Mistakes:

• Using should('contain') on file content
• Checking exact equality instead of substring
• Using property assertion on string