JavaScript Testing 5

Question 1

What is code coverage and which metric measures the percentage of code lines executed by tests?

Accepted Answer

A measure of executed code; statement/line coverage

Answer

Code coverage measures how much source code is executed during tests; statement/line coverage reports the percentage of code lines hit.

Question 2

Which Jest matcher should you use to test that an async function rejects with a specific error?

Accepted Answer

await expect(promise).rejects.toThrow()

Answer

await expect(promise).rejects.toThrow() correctly handles the async rejection and asserts the thrown error type or message.

Question 3

What is the role of JSDOM in Jest tests?

Accepted Answer

It provides a browser-like DOM environment in Node.js for testing UI code

Answer

JSDOM simulates a browser DOM environment in Node.js, allowing Jest to test DOM manipulation code without a real browser.

Question 4

In Cypress, what is the purpose of `cy.intercept()`?

Accepted Answer

To stub, spy on, or modify HTTP requests and responses

Answer

cy.intercept() allows you to stub network requests with mock responses or spy on requests to verify they were made.

Question 5

What is mutation testing in the context of JavaScript?

Accepted Answer

Automatically modifying source code to verify tests catch the changes

Answer

Mutation testing introduces small code changes (mutations) and checks whether existing tests fail, measuring test suite quality.

JavaScript Practice Test