React Jest Interview Questions (2024)
What is Jest, and what are some of its benefits?
How does Jest simulate dependencies?
What distinguishes Enzyme's shallow rendering from its full rendering?
What purpose do snapshots serve in Jest testing?
How can Jest be used to test asynchronous code?
What do Jest's beforeEach and afterEach methods do?
What kinds of matchers are there in Jest?
How do you use Jest to evaluate React components that have state?
How does Jest's describe command work and what is its purpose?
What function does the Jest toHaveBeenCalledWith matcher do?
How can Jest be used to evaluate Redux actions and reducers?
Q: What is Jest, and what are some of its benefits?
Ans:
Facebook created the JavaScript testing tool known as Jest. Testing React apps frequently makes use of it. Fast test run times, automatic module mocking, and integrated code coverage reporting are just a few benefits of Jest.
Q: How does Jest simulate dependencies?
Ans:
Using the mock API that Jest offers, we can build mock versions of your dependencies. To build a
mock implementation of a module or a mock function, use the jest.mock() or jest.fn()
functions,
respectively.
Q: What distinguishes Enzyme's shallow rendering from its full rendering?
Ans:
The top-level component is the only one rendered by shallow rendering in Enzyme; all other descendant components are not rendered. Whereas full rendering displays the complete component tree, including any child components.
Q: What purpose do snapshots serve in Jest testing?
Ans:
In order to evaluate React components, snapshots compare the component's output to a previous snapshot of the component's output. The copy will fail and notify you of any changes if the component's output changes.
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Q: How can Jest be used to test asynchronous code?
Ans:
Asynchronous code can be tested using a number of Jest methods, such as the done()
callback,
async/await, and the .resolves and .rejects matchers.
Q: What do Jest's beforeEach and afterEach methods do?
Ans:
Setting up variables and states are set before each test in beforeEach while cleaup code is written using afterEach methods. Before each test, the beforeEach function is called, and after each test, the afterEach function is called.
Q: What kinds of matchers are there in Jest?
Ans:
- The
.toBe()matcher for equality testing. - The
.toEqual()matcher for object equality testing. - The
.toThrow()matcher for testing errors are just a few of the matchers that Jest offers for testing.
Q: How do you use Jest to evaluate React components that have state?
Ans:
React components with state can be tested using the Jest snapshot testing tool or the Enzyme library, which simulates user interactions and tests the component's functionality.
Using wrapper.state() function we can test the state.
For Example:
test('component state', () => {
const wrapper = shallow(<comp />);
wrapper.setState({ source: 1 });
expect(wrapper.state('source')).exist();
});
Q: How does Jest's describe command work and what is its purpose?
Ans:
While the it function is used to specify individual test cases, the describe function is used to
group together tests that are linked to one another.
Q: What function does the Jest toHaveBeenCalledWith matcher do?
Ans:
To determine whether a function has been called with particular parameters, use the toHaveBeenCalledWith
matcher.
Q: How can Jest be used to evaluate Redux actions and reducers?
Ans:
By building mock implementations of the Redux store and sending actions to the store, user can use Jest to evaluate Redux actions and reducers.