cy.readFile() assertions in Cypress - Test Execution Trace

Test Overview

This test reads a JSON file using cy.readFile() and verifies that the file contains expected data. It checks the presence and correctness of specific keys and values.

Test Code - Cypress

Cypress

describe('Read JSON file and assert contents', () => {
  it('should read the file and verify its content', () => {
    cy.readFile('cypress/fixtures/user.json').then((data) => {
      expect(data).to.have.property('name', 'Alice');
      expect(data).to.have.property('age').that.is.a('number');
      expect(data.hobbies).to.include('reading');
    });
  });
});

Execution Trace - 7 Steps

Step	Action	System State	Assertion	Result
1	Test starts	Cypress test runner is ready	—	PASS
2	Cypress opens test environment	Browser window opens with Cypress test runner UI	—	PASS
3	cy.readFile('cypress/fixtures/user.json') is called	File 'user.json' is accessed in fixtures folder	File is successfully read and parsed as JSON	PASS
4	Assertion: expect(data).to.have.property('name', 'Alice')	Data object contains key 'name' with value 'Alice'	Check that 'name' property equals 'Alice'	PASS
5	Assertion: expect(data).to.have.property('age').and.be.a('number')	Data object contains key 'age' with a numeric value	Check that 'age' property exists and is a number	PASS
6	Assertion: expect(data.hobbies).to.include('reading')	Data object has 'hobbies' array including 'reading'	Check that 'reading' is included in hobbies array	PASS
7	Test ends	All assertions passed, test completes successfully	—	PASS

Failure Scenario

Failing Condition: The file 'user.json' is missing or the 'name' property is not 'Alice'

Execution Trace Quiz - 3 Questions

What does cy.readFile('cypress/fixtures/user.json') do in this test?

A Writes data to the JSON file

B Reads and parses the JSON file from the fixtures folder

C Deletes the JSON file

D Opens a browser window

Key Result

Always verify that the file path is correct and the JSON content matches expected values before asserting properties with cy.readFile().

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