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.