Efficient and Effective Testing with React Library

Increase in complexity of applications also increases the urge to write tests so that a developer can have more confidence about the behavior of the application. So to tackle this, we have a lot of testing libraries out there which can help us write tests for our application.

Today in this article I will talk about a very useful library which can help developers to write tests so easily. We will be discussing the React testing library.
Now you may wonder what the React testing library is? Don’t worry just be with me and we will discuss every aspect of it.

This article is for front-end developers who are looking for testing libraries for React.

What are Test Cases in Applications?

A test case can be defined as a group of actions that can be performed to verify the behavior of the feature of our application. A test case can have testing data, testing steps, postconditions, and preconditions using which a developer can compare the actual and expected results to check whether the application is working as per the requirements.

Why Do We Need a React Testing Library?

React testing is all about what was the requirements and what was delivered. With testing, we can verify if the built-in application meets all the functional, performance, and design requirements that were specified.

Testing is a process that can be used to increase the quality of a software product by identifying errors and problems.

There are cases where human error when executed might cause software failures. When it comes to large and complex applications it is necessary to always push the bug-free code to the production environment. Therefore it requires testing the application throughout the development.

Below are some points that show the importance of React testing for an efficient and bug-free application.

• Testing helps us to detect the bugs before the product is delivered to the client, i.e. guarantees the quality of the software.
• Thoroughly tested applications are reliable and high-performance.
• It makes the software efficient and straightforward to use.

What is the React Testing Library?

React Testing Library is a testing tool that helps developers to test react components. It allows us to test the actual DOM tree rendered on the browser. The goal of this library is to write test cases that resemble how a user would interact with the application, which can give you more confidence about your application functionality.

Let’s start from the ground and find out how we can use the react testing library in our application step by step.

Applications created with react app already include a react testing library but if you want to use it outside the create react app then you can install it with npm.

1. Installation

So the very first thing we need to do is install the react testing library in our application. It’s very simple, we just need to run a npm command.

npm install --save-dev @testing-library/react jest

We are installing jest to run the test code.

2. Create a New React App Using CRA

npx create-react-app react-test-example

Once the application is created you can see a App.test.js file generated inside the src/ folder.

import { render, screen } from '@testing-library/react';
import App from './App';

test('renders learn react link', () => {
render(<App />);
const linkElement = screen.getByText(/learn react/i);
expect(linkElement).toBeInTheDocument();
});
import { render, screen } from '@testing-library/react';
import App from './App';

test('renders learn react link', () => {
render(<App />);
const linkElement = screen.getByText(/learn react/i);
expect(linkElement).toBeInTheDocument();
});

test('renders learn react link', () => {
render(<App />);
screen.debug();
});

The above code includes a render method which virtually renders the app component. To access the rendered HTML we can use screen objects. We can see the results of the render by using screen.debug().

And finally we are asserting whether the link element is present in our document or not using the expect method. When the link is not present, jest will mark the test as failed.

To run test cases we can use the “npm run test” command.

3. React Testing Library Methods for Finding Elements

Most of the time we will use methods to find elements. React testing library provides us several methods to find an element.

• getBytex() : returns an element by its text value.
• getByRole(): return by role attribute.
• getByLabelText(): returns by its label.
• getByTitle(): return by title attribute.

4. Testing User Generated Events

React Testing Library also allows us to test user generated events like button clicks and entering something to a text box.
The user-event library is the companion for simulating user interaction with the browser.
Let us take an example of a toggle button.

import React, { useState } from "react";

function App() {
const [color, setColor] = useState("Red");

const toggleTheme = () => {
const nextTheme = theme === "Red" ? "red" : "yellow";
setTheme(nextTheme);
};

return <button onClick={toggleTheme}>
Current Color: {color}
</button>;
}

export default App;

Now will create a test that finds the button and simulates a click event by using the userEvent.click() method. We can assert the test is by checking the color values.

Advantages

• Prevention from unexpected errors in code
• Reduces the chances of app failures
• Allows developers to focus more on current tasks
• Reduces the need for manual testing