JavaScript Testing 2

Question 1

Which Jest method is used to mock a module's implementation for all tests in a file?

Accepted Answer

jest.mock()

Answer

jest.mock() hoists the mock to the top of the file and replaces the entire module for all tests.

Question 2

What does the `--coverage` flag do when running Jest?

Accepted Answer

Generates a code coverage report

Answer

The --coverage flag instructs Jest to collect and report code coverage statistics for tested files.

Question 3

In Mocha, which hook runs once before all tests in a describe block?

Accepted Answer

before

Answer

The `before` hook in Mocha runs once before all tests within its enclosing describe block.

Question 4

What is a test double in software testing?

Accepted Answer

An object that replaces a real dependency during testing

Answer

A test double is any object substituted for a real dependency — including mocks, stubs, spies, and fakes.

Question 5

Which assertion library method checks that a function throws an error in Jest?

Accepted Answer

expect(fn).toThrow()

Answer

expect(fn).toThrow() verifies that a function throws when called, optionally matching the error message or type.

JavaScript Practice Test