Basic React Testing with Jest and Enzyme

Basic React Testing with Jest and Enzyme

by John Vincent


Posted on June 25, 2018



This stuff ends up sprayed everywhere, so let’s create a reference document.

Introduction

Jest

Enzyme

Github Enzyme

npm i jest  --save-dev

npm i babel-jest babel-core@^7.0.0-0 --save-dev
npm i react-test-renderer --save-dev
npm i enzyme enzyme-adapter-react-16 --save-dev

Visual Studio Code Debugging

For details, see Debugging React with Enzyme and Jest

Configuration

Add to package.json

"jest": {
	"roots": [
		"<rootDir>/src/",
		"<rootDir>/tests/__tests__/"
	],
	"testRegex": "./tests/__tests__/.*.(js|jsx)$",
	"setupTestFrameworkScriptFile": "<rootDir>/tests/setupTests.js",
	"testPathIgnorePatterns": [
		"<rootDir>/tests/__tests__/setup/"
	],
	"moduleNameMapper": {
		"\\.(jpg|jpeg|png|gif|eot|otf|webp|svg|ttf|woff|woff2|mp4|webm|wav|mp3|m4a|aac|oga)$": "<rootDir>/tests/__mocks__/fileMock.js",
		"\\.(css|less|scss)$": "<rootDir>/tests/__mocks__/styleMock.js"
	}
}
  • Mocks images using src/tests/__mocks__/fileMock.js
  • Mocks css, less, scss with src/tests/__mocks__/styleMock.js

Create src/tests/__mocks__/fileMock.js

module.exports = 'test-file-stub';

Create src/tests/__mocks__/styleMock.js

module.exports = {};

Create src/tests/setupTests.js

import Enzyme from 'enzyme';
import Adapter from 'enzyme-adapter-react-16';

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

Create Test code in src/tests/__tests__

Alternative Configuration

I prefer all testing code to be separate.

Choose:

  • tests/__tests__ for test code
  • tests/__mocks__ for mock code

Add to package.json

"jest": {
	"roots": [
		"<rootDir>/src/",
		"<rootDir>/tests/__tests__/"
	],
	"testRegex": "./tests/__tests__/.*.(js|jsx)$",
	"setupTestFrameworkScriptFile": "<rootDir>/src/setupTests.js",
	"testPathIgnorePatterns": [
		"<rootDir>/tests/__tests__/setup/"
	],
	"moduleNameMapper": {
		"\\.(jpg|jpeg|png|gif|eot|otf|webp|svg|ttf|woff|woff2|mp4|webm|wav|mp3|m4a|aac|oga)$": "<rootDir>/tests/__mocks__/fileMock.js",
		"\\.(css|less|scss)$": "<rootDir>/tests/__mocks__/styleMock.js"
	}
},

Test Categories

Focus on the following categories

  • smoke-test
  • content
  • properties-state
  • callbacks-events

Simple Template

/* global describe, it, expect */

import React from 'react';
import { shallow } from 'enzyme';

import { Feedback } from '../../../src/components';

describe('<Feedback />', () => {
	const text = 'Almost got it right';

	describe('smoke-test', () => {
		it('Renders without crashing', () => {
			shallow(<Feedback feedback={text} />);
		});
	});

	describe('properties-state', () => {
	});

	describe('callbacks-events', () => {
	});
		
	describe('content', () => {
	});
});

Run Specific Tests

describe.only will not limit tests.

To limit tests to a specific describe

npm test -- -t '<Help />'

where ‘’ is a label for a specific test suite, for example

describe('<Help />', () => {

To limit tests within a test suite

it.only

Create Tests

Create Test code in /tests/__tests__

Simple Example

Component src/components/Feedback.jsx

import React from 'react';
import PropTypes from 'prop-types';

import './feedback.scss';

const Feedback = props => <h2 className="feedback-title">{props.feedback}</h2>;

Feedback.propTypes = {
	feedback: PropTypes.string.isRequired
};

export default Feedback;

Test Suite tests/__tests__/components/Feedback.jsx

/* global describe, it, expect */

import React from 'react';
import { shallow } from 'enzyme';

import { Feedback } from '../../../src/components';

describe('<Feedback />', () => {
	const text = 'Almost got it right';

	describe('smoke-test', () => {
		it('Renders without crashing', () => {
			shallow(<Feedback feedback={text} />);
		});
	});

	describe('properties-state', () => {
		it('Renders h2', () => {
			const wrapper = shallow(<Feedback feedback={text} />);
			expect(wrapper.find('h2').text()).toEqual(text);
		});
	});

	describe('content', () => {
		it('Renders classname feedback-title', () => {
			const wrapper = shallow(<Feedback feedback={text} />);
			expect(wrapper.hasClass('feedback-title')).toEqual(true);
		});
	});
});

Note

  • Use of find
    • expect(wrapper.find('h2').text()).toEqual(text)
  • Use of hasClass
    • expect(wrapper.hasClass('feedback-title')).toEqual(true)

Callback

Component src/components/Navigation

import React from 'react';
import PropTypes from 'prop-types';

import './navigation.scss';

export default function Navigation(props) {
	return (
		<header className="navigation">
			<nav>
				<ul className="clearfix">
					<li>
						<button onClick={props.toggleHelp}>What?</button>
					</li>
					<li>
						<button onClick={props.toggleGame}>+ New Game</button>
					</li>
				</ul>
			</nav>
			<h1>HOT or COLD</h1>
		</header>
	);
}

Navigation.propTypes = {
	toggleHelp: PropTypes.func.isRequired,
	toggleGame: PropTypes.func.isRequired
};

Tests

describe('callbacks-events', () => {
	describe('help button', () => {
		it('Find the button', () => {
			const wrapper = shallow(<Navigation toggleHelp={toggleHelp} toggleGame={toggleGame} />);
			expect(
				wrapper
					.find('button')
					.first()
					.text()
			).toEqual('What?');
		});
		it('Fire the button', () => {
			const callback = jest.fn();
			const wrapper = shallow(<Navigation toggleHelp={callback} toggleGame={toggleGame} />);
			expect(callback).not.toHaveBeenCalled();
			wrapper
				.find('button')
				.first()
				.simulate('click');
			expect(callback).toHaveBeenCalled();
		});
	});

Useful Syntax

expect(wrapper.find('button').first().text()).toEqual('What?');			

Example

Component src/components/GuessForm.jsx

import React from 'react';
import PropTypes from 'prop-types';

import './guessForm.scss';

export default class GuessForm extends React.Component {
	constructor(props) {
		super(props);
		this.state = {
			showAnswer: false
		};
	}

	handleGuess = () => {
		const input = this.guessInput.value;
		if (input === '?') {
			this.toggleAnswer();
			return;
		}

		const guess = parseInt(input, 10);
		if (!Number.isNaN(guess)) {
			const num = guess * 1;
			if (num > 0 && num < 100) {
				this.props.handleGuess(num);
			}
		}
		this.guessInput.value = '';
	};

	toggleAnswer() {
		this.setState({ showAnswer: !this.state.showAnswer });
	}

	render() {
		return (
			<div>
				{!this.props.victory && (
					<form className="guessForm" onSubmit={e => e.preventDefault()}>
						<input
							type="text"
							name="userGuess"
							id="userGuess"
							className="text"
							maxLength="3"
							autoComplete="off"
							placeholder="Enter your Guess"
							ref={input => {
								this.guessInput = input;
							}}
							autoFocus
						/>
						<button onClick={this.handleGuess}>Guess</button>
					</form>
				)}
				{this.state.showAnswer && <p>Answer is {this.props.answer}</p>}
			</div>
		);
	}
}

GuessForm.propTypes = {
	handleGuess: PropTypes.func.isRequired,
	answer: PropTypes.number.isRequired,
	victory: PropTypes.bool.isRequired
};

Test __tests__/components/GuessForm.jsx

//

/* global describe, it, jest, expect */

import React from 'react';
import { shallow, mount } from 'enzyme';

import { GuessForm } from '../../../src/components';

describe('<GuessForm />', () => {
	const handleGuess = jest.fn();
	const answer = 79;
	const victory = false;

	describe('smoke-test', () => {
		it('Renders without crashing', () => {
			shallow(<GuessForm handleGuess={handleGuess} answer={answer} victory={victory} />);
		});
	});

	describe('content', () => {
		it('Renders classname guessForm', () => {
			const wrapper = shallow(
				<GuessForm handleGuess={handleGuess} answer={answer} victory={victory} />
			);
			expect(wrapper.find('form').hasClass('guessForm')).toEqual(true);
			expect(wrapper.find('p').exists()).toBeFalsy();
		});
	});

	describe('properties-state', () => {
		it('Check state', () => {
			const wrapper = shallow(
				<GuessForm handleGuess={handleGuess} answer={answer} victory={victory} />
			);
			expect(wrapper.state().showAnswer).toEqual(false);
		});

		it('Victory found', () => {
			const truth = true;
			const wrapper = shallow(
				<GuessForm handleGuess={handleGuess} answer={answer} victory={truth} />
			);
			expect(wrapper.find('form').exists()).toBeFalsy();
		});

		it('Find the button', () => {
			const wrapper = shallow(
				<GuessForm handleGuess={handleGuess} answer={answer} victory={victory} />
			);
			expect(wrapper.find('button').text()).toEqual('Guess');
		});
	});

	describe('callbacks-events', () => {
		it('Find the button', () => {
			const callback = jest.fn();
			mount(<GuessForm handleGuess={callback} answer={answer} victory={victory} />);
			expect(callback).not.toHaveBeenCalled();
		});

		it('Fire the button', () => {
			const callback = jest.fn();
			const wrapper = mount(<GuessForm handleGuess={callback} answer={answer} victory={victory} />);
			const value = 10;
			wrapper.find('input[type="text"]').instance().value = value;
			expect(wrapper.find('button').text()).toEqual('Guess');
			wrapper.find('button').simulate('click');
			expect(callback).toHaveBeenCalled();
			expect(callback).toHaveBeenCalledWith(value);
		});

		it('Should reset input', () => {
			const callback = jest.fn();
			const wrapper = mount(<GuessForm handleGuess={callback} answer={answer} victory={victory} />);
			const input = wrapper.find('input[type="text"]');
			input.instance().value = 10;
			wrapper.find('button').simulate('click');
			expect(input.instance().value).toEqual('');
		});

		it('Ask for Help', () => {
			const callback = jest.fn();
			const wrapper = mount(<GuessForm handleGuess={callback} answer={answer} victory={victory} />);
			expect(wrapper.find('p').exists()).toBeFalsy();
			wrapper.find('input[type="text"]').instance().value = '?';
			wrapper.find('button').simulate('click');
			expect(callback).not.toHaveBeenCalled();
			expect(wrapper.state().showAnswer).toEqual(true);
			expect(wrapper.find('p').exists()).toBeTruthy();

			wrapper.find('button').simulate('click');
			expect(callback).not.toHaveBeenCalled();
			expect(wrapper.state().showAnswer).toEqual(false);
			expect(wrapper.find('p').exists()).toBeFalsy();
		});
	});
});

Note

  • React.Fragment was not working
  • Properties need to be provided
  • Functions can be mocked using jest.fn()