Component test setup in Cypress - Test Execution Trace

Test Overview

This test sets up a simple React component in Cypress for testing. It verifies that the component renders correctly with the expected text.

Test Code - Cypress

Cypress

import React from 'react';
import { mount } from 'cypress/react18';

function Greeting({ name }) {
  return <h1>Hello, {name}!</h1>;
}

describe('Greeting component', () => {
  it('renders greeting message', () => {
    mount(<Greeting name="Alice" />);
    cy.get('h1').should('contain.text', 'Hello, Alice!');
  });
});

Execution Trace - 4 Steps

Step	Action	System State	Assertion	Result
1	Test starts	Cypress test runner is ready	—	PASS
2	Mount the Greeting component with prop name='Alice'	React component Greeting is rendered inside Cypress iframe	—	PASS
3	Find the <h1> element	The DOM contains <h1>Hello, Alice!</h1>	cy.get('h1') locates the heading element	PASS
4	Check that <h1> contains text 'Hello, Alice!'	The heading text is visible	cy.get('h1').should('contain.text', 'Hello, Alice!') verifies correct text	PASS

Failure Scenario

Failing Condition: The component does not render or the text is incorrect

Execution Trace Quiz - 3 Questions

What does the mount() function do in this test?

A It renders the React component inside Cypress for testing

B It clicks a button in the component

C It navigates to a new page

D It waits for an element to appear

Key Result

Always verify your component is properly mounted with the correct props before asserting on its rendered output in component tests.

Practice

1. What is the main purpose of using mount() in Cypress component testing?

easy

A. To write unit tests for backend APIs

B. To run end-to-end tests on the whole application

C. To load a component inside Cypress for testing

D. To deploy the application to a server

Solution

1. Step 1: Understand the role of mount()

   mount() is used to load a UI component inside Cypress so you can test it in isolation.

2. Step 2: Differentiate from other test types

   End-to-end tests run the whole app, but mount() focuses on small parts (components).

3. Final Answer:

   To load a component inside Cypress for testing -> Option C

4. Quick Check:

   mount() loads component [OK]

Hint: Remember: mount() loads components, not full apps [OK]

Common Mistakes:

• Confusing mount() with full app testing
• Thinking mount() deploys code
• Mixing component and API testing

2. Which of the following is the correct syntax to prepare a component before each test in Cypress?

easy

A. beforeEach(() => { mount() })

B. beforeAll(() => { mount() })

C. afterEach(() => { mount() })

D. before(() => { mount() })

Solution

1. Step 1: Identify the correct hook for setup before each test

   beforeEach() runs before every test, ideal for fresh component setup.

2. Step 2: Confirm syntax correctness

   The syntax beforeEach(() => { mount(<MyComponent />) }) correctly mounts the component before each test.

3. Final Answer:

   beforeEach(() => { mount(<MyComponent />) }) -> Option A

4. Quick Check:

   Use beforeEach() for setup [OK]

Hint: Use beforeEach() to reset component before every test [OK]

Common Mistakes:

• Using beforeAll() which runs only once
• Using afterEach() which runs after tests
• Using before() which is deprecated in Cypress

3. Given this Cypress component test code, what will be the output in the test runner?

describe('Button component', () => {
  beforeEach(() => {
    mount(Click me)
  })

  it('checks button text', () => {
    cy.get('button').should('have.text', 'Click me')
  })
})

medium

A. Test passes because button text matches

B. Test fails because button text is missing

C. Test errors due to wrong selector syntax

D. Test is skipped because mount() is missing

Solution

1. Step 1: Analyze the mount and selector

   The mount() loads a button with text 'Click me'. The selector cy.get('button') correctly targets it.

2. Step 2: Check the assertion

   The assertion should('have.text', 'Click me') matches the button's text exactly, so it passes.

3. Final Answer:

   Test passes because button text matches -> Option A

4. Quick Check:

   Correct selector and text = pass [OK]

Hint: Match selector text exactly for passing assertion [OK]

Common Mistakes:

• Using wrong selector causing no element found
• Mismatching text in assertion
• Forgetting to mount component before test

4. Identify the error in this Cypress component test setup:

describe('Input component', () => {
  beforeEach(() => {
    mount('')
  })

  it('checks placeholder', () => {
    cy.get('input').should('have.attr', 'placeholder', 'Enter name')
  })
})

medium

A. beforeEach() should be replaced with afterEach()

B. mount() should receive JSX, not a string

C. cy.get() selector is incorrect

D. The placeholder attribute is misspelled

Solution

1. Step 1: Check the argument passed to mount()

   The code passes a string '<input placeholder="Enter name" />' instead of JSX element. mount() expects JSX, not a string.

2. Step 2: Confirm other parts are correct

   The selector cy.get('input') and attribute check are correct, so no error there.

3. Final Answer:

   mount() should receive JSX, not a string -> Option B

4. Quick Check:

   mount() needs JSX, not string [OK]

Hint: Pass JSX, not strings, to mount() [OK]

Common Mistakes:

• Passing HTML strings instead of JSX to mount()
• Confusing beforeEach() with afterEach()
• Using wrong selectors

5. You want to test a component that renders a list of items passed as props. Which setup correctly mounts the component with props before each test?

hard

A. beforeEach(() => { mount() })

B. beforeEach(() => { mount('') })

C. beforeEach(() => { mount(List, { props: { items: ["a", "b"] } }) })

D. beforeEach(() => { mount() })

Solution

1. Step 1: Understand correct JSX with props

   Passing props in JSX uses syntax like <List items={["a", "b"]} />. This is correct in beforeEach(() => { mount(<List items={["a", "b"]} />) }).

2. Step 2: Identify incorrect options

   beforeEach(() => { mount('<List items=["a", "b"] />') }) passes a string, not JSX. beforeEach(() => { mount(List, { props: { items: ["a", "b"] } }) }) uses wrong mount signature. beforeEach(() => { mount(<List items="a,b" />) }) passes a string instead of array.

3. Final Answer:

   beforeEach(() => { mount(<List items={["a", "b"]} />) }) -> Option D

4. Quick Check:

   Use JSX with array props [OK]

Hint: Pass props as JSX arrays, not strings [OK]

Common Mistakes:

• Passing component as string instead of JSX
• Using wrong mount function signature
• Passing props as comma-separated string