20 React Testing Library Interview Questions and Answers

React Testing Library is a popular tool for testing React applications. If you’re applying for a position that involves React, it’s likely that you’ll be asked about React Testing Library during your interview. In this article, we review some of the most common React Testing Library questions and how you should answer them.

React Testing Library Interview Questions and Answers

Here are 20 commonly asked React Testing Library interview questions and answers to prepare you for your interview:

1. What is React Testing Library?

React Testing Library is a library for testing React components. It is designed to help you test React components in a way that is similar to how the components are used in the application. This library is a replacement for the existing React TestUtils library.

2. Why should you use the React testing library instead of other solutions?

The React testing library is a great solution because it is designed to test React components in a way that is similar to how the components are used in the application. This makes it easy to ensure that your tests are accurate and that they cover all the functionality of your components.

3. How would you write tests for a component that makes API calls?

You would want to mock out the API calls so that the tests are not actually making real API calls. This way, you can control the data that is returned and test how the component behaves in different scenarios.

4. Can you explain what fireEvent does in React testing library?

FireEvent is a function that allows you to fire events on a given element. This is useful for testing purposes, as you can simulate user interactions and test how your component responds.

5. How do you test components that have child components?

You can use the React Testing Library to test child components by using the findBy* methods. For example, you can use the findByTestId method to find a child component by its test id. You can then use the methods on the React Testing Library to test the child component as you would any other component.

6. What happens when you try to render or mount an unconnected component using ReactDOM?

If you try to render or mount an unconnected component using ReactDOM, you will get an error that says “Uncaught InvariationError: connect(): Unexpected invocation.” This is because ReactDOM doesn’t know how to connect the component to the store, so it can’t render it.

7. Does ReactDOM support hooks? If yes, then how?

Yes, ReactDOM does support hooks. The way that ReactDOM supports hooks is by allowing you to use the same hooks that are available in ReactJS in your ReactDOM components. This means that you can use the useState, useEffect, and useContext hooks in your ReactDOM components just like you would in ReactJS components.

8. What’s the difference between rendering and mounting components with ReactDOM?

When you render a component with ReactDOM, it is rendered as a static HTML element. This means that it cannot be interacted with and will not change if the underlying data changes. When you mount a component with ReactDOM, it is rendered as a dynamic HTML element. This means that it can be interacted with and will change if the underlying data changes.

9. Can you give me some examples of real-world applications where ReactDOM has been used?

ReactDOM has been used in many different applications, including Facebook, Instagram, Netflix, and the New York Times.

10. What are some common features found in most implementations of ReactDOM?

The most common features found in ReactDOM implementations include the ability to render React components to an HTML DOM, to handle events on the DOM, and to update the DOM in response to changes in the React component tree.

11. What are the main components of ReactDOM?

The main components of ReactDOM are the React element, the React component, and the ReactDOM renderer. The React element is the basic unit of React, and is what is rendered by the ReactDOM renderer. The React component is a higher-level abstraction that represents a reusable piece of UI. Finally, the ReactDOM renderer is responsible for actually rendering React elements into the DOM.

12. Is it possible to make ReactDOM more accessible? If so, can you describe your approach?

Yes, it is possible to make ReactDOM more accessible. One approach is to use the React Testing Library, which is a library that provides helper functions to make it easier to test React components. The library includes a function called “renderIntoDocument” which renders a React component into a DOM node, making it easier to test.

13. What is a stateful component in ReactDOM?

A stateful component is a component that maintains its own internal state. This internal state can be changed over time, and the component will re-render itself to reflect these changes. Stateful components are typically used to represent interactive elements on a page, such as form fields or buttons.

14. What’s the difference between a functional component and a class component in ReactDOM? Why is one preferred over another?

Functional components are preferred over class components because they are simpler and easier to read. They are also more efficient because they don’t have to re-render when props or state changes.

15. Where are class methods defined in ReactDOM?

Class methods are defined in the ReactDOM.Component class.

16. Which event handler is called first: onClick() or onKeyUp()?

onClick() is called first.

17. What do you understand about refs in ReactDOM?

Refs are a way to access the underlying DOM nodes of a React component. This can be useful if you need to programmatically manipulate the DOM, for instance to focus an input field.

18. What are lifecycle methods in ReactDOM?

The lifecycle methods in ReactDOM are:

– componentWillMount
– componentDidMount
– componentWillReceiveProps
– shouldComponentUpdate
– componentWillUpdate
– componentDidUpdate
– componentWillUnmount

19. What are the different phases in the life cycle of a ReactDOM component?

The life cycle of a ReactDOM component can be divided into three distinct phases:

1) The initial phase, where the component is created and inserted into the DOM.

2) The update phase, where the component is updated in response to changes in props or state.

3) The unmounting phase, where the component is removed from the DOM.

20. When do you need to use the key attribute for a component in ReactDOM?

The key attribute is used in ReactDOM when you want to uniquely identify a component. This is especially important when you are working with dynamic components that are being created and destroyed on the fly. By assigning a key to each component, you can make sure that React knows which component is which, and can correctly update the UI.