1. Iteration Speed
   Many tools offer a quick feedback loop between changes done and displaying the results. But these tools may not model the browser precisely. So, tools like Jest are recommended for good iteration speed.
2. Requirement of Realistic Environment
   Some tools use a realistic browser environment but they reduce the iteration speed. React testing Libraries like mocha work well in a realistic environment. 
3. Component Dependencies
   Some react components have dependencies for the modules that may not work best in the testing environment. So, carefully mocking these modules out with proper replacements are required. Tools and libraries like Jest support mocking modules. 
4. Flow Length
   To test a long flow, frameworks and libraries like Cypress, Playwright, and Puppeteer are used to navigate between multiple assets and routes.

Best React Testing Libraries and Tools

1. Jest

1.1 Features of Jest

• When it comes to JavaScript projects, Jest is meant to run without any further configuration.
• Individual test procedures are started in parallel to increase throughput.
• Quick and risk-free.
• Entire toolkit of Jest is presented at one place. It is well documented and well maintained. 
• Including untested files, Jest collects code coverage information from entire projects. 

1.2 How to Install Jest?

 
npm install --save-dev jest
or
yarn add --dev jest

1.3 First Test Using Jest:

    function add(x, y) {
        return x+y;
    }
    module.exports = add;      

    const add = require('./add');

    test('adds 2 + 2 to equal 4', () => {
    expect(add(1, 2)).toBe(4);
    });

    function add(x, y) {
        return x+y;
      }
      module.exports = add;      

2. React Testing Library

2.1 Features of React Testing Library

• Very light-weight
• It has inbuilt DOM testing utilities
• More accessible library

2.2 How to Install React Testing Library?

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

    yarn add --dev @testing-library/react

    npm install --save-dev @testing-library/react@12

    yarn add --dev @testing-library/react@12

    import React from "react";

    export const App = () => Hello World!;

    import React from "react";
    import { render } from "@testing-library/react";
    import { firstApp } from "./firstApp";

    describe("App Component", function () {
    it("should have Hello World! string", function () {
        let { getByText } = render();
        expect(getByText("Hello world!")).toMatchInlineSnapshot(`
        
            Hello World!
        
        `);
    });
    });

3. Chai

3.1 Features of Chai

• Chai allows software testers to perform various types of assertions.
  • Expect
  • Assert
  • Should
• The Chai expect and Should styles are used to chain the natural language assertions together. The only difference is chai should style extends “should” with each property. 
• The Chai assert style offers the developer with a standard assert-dot notation comparable to what is included with node.js.
• The assert style component additionally offers further tests and browser support.

3.2 How to Install Chai?

    $ npm install --save-dev chai

3.3 First Test Using Chai:

    var chai = require('chai');  
    var assert = chai.assert;    // Using Assert style
    var expect = chai.expect;    // Using Expect style
    var should = chai.should();  // Using Should style

    function app(int a, int b){
        return a*b;
    }    

    describe(“Multiplication”, () => {
        it(“Multiplies 2 and 3”, () => {
        chai.expect(app(2,3).to.equal(6);
    });
    it(“Multiplies 4 and 2”, () => {
        chai.expect(app(4,2).to.equal(7);
    });
    });    

4. Mocha

4.1 Features of Mocha

• Capabilities to test synchronous and asynchronous programs using a simple interface.
• Versatile and precise analysis
• The capacity to execute tests in a linear manner while monitoring for and reacting to undetected exceptions by tracing them to test cases.
• Ability to execute functions in a predetermined order and record the results to a terminal window.
• Software state is automatically cleaned up so that test cases can run separately from  one another.

4.2 How to Install Mocha?

    npm i --save-dev mocha

    yarn add mocha

    {
        "scripts": {
          "test": "mocha"
        }
      }      

4.3 First Test Using Mocha:

    // test/test.js

    var modal = require('modal');
    describe('Array', function() {
    describe('#indexOf()', function() {
        it('should return 0 when the value is not present', function() {
        assert.equal([5, 4, 3, 2, 1].indexOf(6), -3);
        });
    });
    });

5. Cypress.io

5.1 Features of Cypress

• Cypress records snapshots over the course of your test runs.
• Rapid debugging is possible because of the clearly shown errors and stack traces.
• Cypress will patiently wait for your instructions and statements.
• Testing that is quick, consistent, and dependable without any hiccups is desirable.

5.2 How to Install Cypress​?

    npm create vite@latest my-awesome-app -- --template react

    cd my-awesome-app
    npm install

    npm install cypress -D

    npx cypress open

5.3 First Test Using Cypress:

    src/components/Stepper.cy.jsx
    import React from 'react'
    import Stepper from './Stepper'
    
    describe('', () => {
     it('renders', () => {
       // Check : https://on.cypress.io/mounting-react
       cy.mount()
     })
    })    

6. Jasmine

6.1 Features of Jasmine

• It’s quick, has little overhead, and doesn’t rely on anything except itself.
• It provides almost every functionalities and features that one requires to test the code. 
• You may use it with the browser or Node.
• It’s compatible with Python and Ruby also.
• In other words, the DOM is not necessary.
• It has a simple syntax and an extensive API that is easy to use.
• The tests and their outcomes can be described in ordinary terms.

6.2 How to Install Jasmine?

    npm install - - save - dev @babel/core \
                                @babel/register \
                                babel-preset-react-app \
                                cross-env \
                                jsdom \
                                jasmine

OR 

yarn add - - dev babel-cli \
            @babel/register \
            babel-preset-react-app \
            cross-env \
            enzyme \
            enzyme-adapter-react-16 \
            jasmine-enzyme \
            jsdom \
            jasmine

    // For NPM 
    npm jasmine init 

    // For Yarn 
    yarn run jasmine init

6.3 First Test Using Jasmine

    // babel.js
    require('@babel/register');

    // for typescript
    require('@babel/register')({
        "extensions": [".ts", ".tsx", ".js", ".jsx"]
    });


    describe("A suite is a function", function() {
    // For grouping related specs, there is a describe function. 
    // Typically each test file has one describe function at the top level.   

    let x;

        it("and so is a spec", function() { 
    // Specs are defined by calling the global Jasmine function it.
            x = true;
            expect(x).toBe(true);
        });
    });

    describe("The 'toBe' compares with ===", function() {

    it("and has a negative case", function() {
            expect(false).not.toBe(true);
        });

    it("and has a positive case", function() {
            expect(true).toBe(true);
        });

    });

7. Enzyme

7.1 Features of Enzyme

• Enzyme’s API aims to be user-friendly and adaptable by modeling itself after jQuery’s API for DOM manipulation and traversal.
• The Enzyme Application Programming Interface allows for the Inspection of React Elements.
• It provides shallow rendering.
• Provides access to enterprise implementations of your component.
• Provides execution of a complete DOM rendering.
• There are cases where using react-hooks in shallow rendering is appropriate.

7.2 How to Install Enzyme?

    npm - - save - dev enzyme enzyme-adapter-react-16

7.3 First Test Using Enzyme

    npm install –save-dev enzyme

    import React, { Component } from 'react';
    import './App.scss';

    class App extends React.Component {
    constructor(props: any) {
        super(props);
        this.state = {        
        };
    }
    render() {
        return (
        
       
            Click Here
        
        )
    }
    };

    export default App;

    import React from 'react'
    import Enzyme, { shallow } from 'enzyme'
    import Adapter from 'enzyme-adapter-react-16'
    import App from './App'

    Enzyme.configure({ adapter: new Adapter() })

    describe('First Test Case', () => {
    it('it should render button', () => {
        const wrapper = shallow()
        const buttonElement  = wrapper.find('#ClickHere');
        expect(buttonElement).toHaveLength(1);
        expect(buttonElement.text()).toEqual('Click Here');
    })
    })

8. Conclusion