cy.readFile() assertions in Cypress - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ assertion

intermediate

Correct assertion for JSON file content

You use cy.readFile('data.json') to read a JSON file. Which assertion correctly checks that the file contains a key status with value success?

Cypress

cy.readFile('data.json').then((data) => {
  // Which assertion is correct here?
});

A expect(data['status']).to.be.true

B expect(data.status).to.equal('success')

C expect(data.status).to.be.undefined

D expect(data.status).to.have.length(7)

💡 Hint

Check the exact value of the key, not its type or length.

The key 'status' should have the string value 'success'. Option B checks for exact equality. Option B wrongly expects a boolean true. Option B expects undefined which is incorrect. Option B expects a length which is invalid for a string value check.

❓ Predict Output

intermediate

Output of reading a text file and asserting content

Given a text file message.txt containing the text Hello World, what will be the result of this test code?

Cypress

cy.readFile('message.txt').should('contain', 'World')

A Test passes because 'World' is part of the file content

B Test fails because 'contain' is not a valid assertion

C Test fails because 'Hello' is missing

D Test throws an error because file is not JSON

💡 Hint

The assertion checks if the file content includes the substring.

The 'should' assertion with 'contain' checks if the string includes the given substring. Since 'World' is in 'Hello World', the test passes. The file being text is fine for this assertion.

🔧 Debug

advanced

Why does this cy.readFile() assertion fail?

You run this code but the test fails. Why?

Cypress

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

A The key 'enabled' is a string 'true', not boolean true

B cy.readFile cannot read JSON files

C The assertion syntax is incorrect

D The file path is wrong

💡 Hint

Check the data type of the value in the JSON file.

If the JSON file has "enabled": "true" (string), the assertion expecting boolean true fails. The assertion syntax and file reading are correct. The file path is assumed correct.

🧠 Conceptual

advanced

Best practice for asserting large JSON file content

You read a large JSON file with cy.readFile('large.json'). Which approach is best to assert that the file contains a key version with value 1.2.3 without loading the entire file into memory?

A Use <code>cy.readFile('large.json').should('contain', '"version":"1.2.3"')</code>

B Read the whole file and use <code>expect(data.version).to.equal('1.2.3')</code>

C Use <code>cy.readFile('large.json').its('version').should('equal', '1.2.3')</code>

D Manually parse the file line by line with <code>cy.readFile</code>

💡 Hint

Use Cypress chaining to access nested properties efficiently.

Option C uses its() to directly access the 'version' key, which is efficient and readable. Option C reads the whole file and then asserts, which is less efficient. Option C checks for a string pattern which is brittle. Option C is not supported by cy.readFile.

❓ framework

expert

Handling asynchronous assertion failures with cy.readFile()

You want to retry reading a file until it contains a key ready set to true. Which Cypress code snippet correctly implements this retry logic?

A cy.readFile('status.json').should((data) => { expect(data.ready).to.be.true })

B cy.readFile('status.json').then((data) => { if (!data.ready) throw new Error('Not ready') })

C cy.readFile('status.json').should('equal', { ready: true })

D cy.readFile('status.json').should('have.property', 'ready', true)

💡 Hint

Use built-in Cypress assertions that support automatic retry.

Option D uses 'should' with 'have.property' which Cypress retries automatically until the condition is met or timeout. Option D uses a callback but may not retry properly. Option D throws error manually but does not leverage Cypress retry. Option D expects exact object equality which may fail if other keys exist.

Practice

1. What does cy.readFile() do in Cypress testing?

easy

A. Writes data to a file during the test

B. Reads the content of a file so you can check its data

C. Deletes a file from the system

D. Uploads a file to a server

Solution

1. Step 1: Understand the purpose of cy.readFile()

   This command is used to read the contents of a file during a Cypress test.

2. Step 2: Identify what cy.readFile() does not do

   It does not write, delete, or upload files; it only reads them.

3. Final Answer:

   Reads the content of a file so you can check its data -> Option B

4. Quick Check:

   cy.readFile() = Read file content [OK]

Hint: Remember: readFile reads, not writes or deletes [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 assert that a file contains the text "Hello World" using cy.readFile()?

easy

A. cy.readFile('file.txt').should('containText', 'Hello World')

B. cy.readFile('file.txt').should('equals', 'Hello World')

C. cy.readFile('file.txt').should('includes', 'Hello World')

D. cy.readFile('file.txt').should('contain', 'Hello World')

Solution

1. Step 1: Identify the correct assertion method for substring check

   The correct assertion to check if a string contains text is contain.

2. Step 2: Match syntax with Cypress documentation

   should('contain', 'text') is the valid syntax; others like 'equals', 'includes', or 'containText' are incorrect here.

3. Final Answer:

   cy.readFile('file.txt').should('contain', 'Hello World') -> Option D

4. Quick Check:

   Use 'contain' for substring assertions [OK]

Hint: Use 'contain' to check if file text includes a string [OK]

Common Mistakes:

• Using 'equals' instead of 'contain' for substring
• Using 'includes' which is not a Cypress assertion
• Using 'containText' which is for DOM elements

3. Given the file data.json contains {"name": "Alice", "age": 30}, what will this test assertion do?

cy.readFile('data.json').should('deep.equal', { name: 'Alice', age: 30 })

medium

A. Pass because the file content matches the object exactly

B. Fail because the object keys are strings in the file

C. Fail because 'deep.equal' cannot compare objects

D. Pass but only if the file is a string, not JSON

Solution

1. Step 1: Understand deep.equal assertion

   This assertion checks if two objects have the same structure and values deeply.

2. Step 2: Check if cy.readFile() parses JSON automatically

   Yes, it parses JSON files into objects, so the assertion compares objects correctly.

3. Final Answer:

   Pass because the file content matches the object exactly -> Option A

4. Quick Check:

   deep.equal compares objects deeply [OK]

Hint: Use deep.equal to compare JSON objects, not strings [OK]

Common Mistakes:

• Thinking file content is a string, not parsed JSON
• Confusing deep.equal with shallow equal
• Assuming keys must be non-string

4. What is wrong with this Cypress test code?

cy.readFile('log.txt').should('include', 'Error')

medium

A. The file must be JSON to use should assertions

B. The file path must be absolute, not relative

C. The assertion method should be 'contain', not 'include'

D. The method 'include' is correct and will pass if 'Error' is found

Solution

1. Step 1: Check the assertion method name

   Cypress uses 'contain' for substring assertions; 'include' is not a valid assertion method.

2. Step 2: Confirm correct assertion for substring

   The correct method is 'contain' to check if text includes a substring.

3. Final Answer:

   The assertion method should be 'contain', not 'include' -> Option C

4. Quick Check:

   Use 'contain' for substring assertions, not 'include' [OK]

Hint: Use 'contain' for substring checks, not 'include' [OK]

Common Mistakes:

• Using 'include' instead of 'contain'
• Thinking relative paths are invalid
• Assuming only JSON files can be read

5. You want to verify a downloaded CSV file contains the header row exactly as "Name,Age,Email". Which Cypress code correctly reads the file and asserts this?

hard

A. cy.readFile('downloads/data.csv').should('contain', 'Name,Age,Email')

B. cy.readFile('downloads/data.csv').should('equal', 'Name,Age,Email')

C. cy.readFile('downloads/data.csv').should('deep.equal', 'Name,Age,Email')

D. cy.readFile('downloads/data.csv').should('include', 'Name,Age,Email')

Solution

1. Step 1: Understand the file content and assertion needed

   The CSV file is text, and we want to check if it contains the exact header row as a substring.

2. Step 2: Choose the correct assertion for substring in text files

   contain is the correct assertion to check if the file text includes the header row.

3. Final Answer:

   cy.readFile('downloads/data.csv').should('contain', 'Name,Age,Email') -> Option A

4. Quick Check:

   Use 'contain' to check text includes header row [OK]

Hint: Use 'contain' to check CSV header text inside file [OK]

Common Mistakes:

• Using 'equal' which requires exact full file match
• Using 'deep.equal' which is for objects, not strings
• Using 'include' which is not a valid assertion