How to Use React Testing Library

In this video we'll learn how to use react testing library to query elements from the DOM and interact with those elements. We also use the user-events package from the react testing library ecosystem to make our interactions easier!

In the initial part of this video we will be adding tests to an existent component.

In the second part of the video, we will add a new feature to our component using TDD (Test Driven Development)

react testing library = @testing-library/react npm package

 

Timeline: 
00:00 Agenda
01:03 TDD: Red, Green, Refactor
02:30 Intro to React Testing Library
03:45 The more your tests resemble the way your software is used,
the more confidence they can give you.
04:32 Queries and Priority
05:45 Automated Query Selector for us: Playground
07:27 Code
23:00 TDD: New Feature

What is GEEK

Buddha Community

How native is React Native? | React Native vs Native App Development

If you are undertaking a mobile app development for your start-up or enterprise, you are likely wondering whether to use React Native. As a popular development framework, React Native helps you to develop near-native mobile apps. However, you are probably also wondering how close you can get to a native app by using React Native. How native is React Native?

In the article, we discuss the similarities between native mobile development and development using React Native. We also touch upon where they differ and how to bridge the gaps. Read on.

A brief introduction to React Native

Let’s briefly set the context first. We will briefly touch upon what React Native is and how it differs from earlier hybrid frameworks.

React Native is a popular JavaScript framework that Facebook has created. You can use this open-source framework to code natively rendering Android and iOS mobile apps. You can use it to develop web apps too.

Facebook has developed React Native based on React, its JavaScript library. The first release of React Native came in March 2015. At the time of writing this article, the latest stable release of React Native is 0.62.0, and it was released in March 2020.

Although relatively new, React Native has acquired a high degree of popularity. The “Stack Overflow Developer Survey 2019” report identifies it as the 8th most loved framework. Facebook, Walmart, and Bloomberg are some of the top companies that use React Native.

The popularity of React Native comes from its advantages. Some of its advantages are as follows:

• Performance: It delivers optimal performance.
• Cross-platform development: You can develop both Android and iOS apps with it. The reuse of code expedites development and reduces costs.
• UI design: React Native enables you to design simple and responsive UI for your mobile app.
• 3rd party plugins: This framework supports 3rd party plugins.
• Developer community: A vibrant community of developers support React Native.

Why React Native is fundamentally different from earlier hybrid frameworks

Are you wondering whether React Native is just another of those hybrid frameworks like Ionic or Cordova? It’s not! React Native is fundamentally different from these earlier hybrid frameworks.

React Native is very close to native. Consider the following aspects as described on the React Native website:

• Access to many native platforms features: The primitives of React Native render to native platform UI. This means that your React Native app will use many native platform APIs as native apps would do.
• Near-native user experience: React Native provides several native components, and these are platform agnostic.
• The ease of accessing native APIs: React Native uses a declarative UI paradigm. This enables React Native to interact easily with native platform APIs since React Native wraps existing native code.

Due to these factors, React Native offers many more advantages compared to those earlier hybrid frameworks. We now review them.

#android app #frontend #ios app #mobile app development #benefits of react native #is react native good for mobile app development #native vs #pros and cons of react native #react mobile development #react native development #react native experience #react native framework #react native ios vs android #react native pros and cons #react native vs android #react native vs native #react native vs native performance #react vs native #why react native #why use react native

Interaction Testing with React Testing Library

Testing is complicated. I’ve certainly never been good at it. For the longest time, I’ve only been focused on basic function input-output unit tests. Why? Because they were easy — you didn’t need to render HTML, you didn’t need to query DOM elements, you didn’t need to interact with said DOM elements. But of course, React component testing is a necessity for any mature codebase. And it finally came time for me to sit down and figure it out.

That’s when I discovered React Testing Library. And suddenly, everything seemingly became much simpler. All the complexities that I’ve encountered, but not understood, that made me put off React component testing disappeared. Hopefully, the same will happen for you.

#react-testing-library #unit-testing #react #jest #interaction-testing

Test Driven Development (TDD) with React Testing Library & Mock Service Worker

Let’s step up our testing game with two useful libraries that lend themselves excellently to a TDD approach.

Setting up

Whenever I want to try out something React-related, I use the library create-react-app. It gives you a ready-to-work-with basic React application with no configuration needed. Recent versions also come bundled with React Testing Library, so if you use the latest create-react-app, you can start using React Testing Library straight away. If not — install @testing-library/react and @testing-library/jest-dom in your existing React application.

I am going to implement the following functionality: a simple recipe list with a search function. It will look something like this to a user in a mobile browser:

Image credits: Burger Photo by Robin Stickel on Unsplash, French Toast Photo by Joseph Gonzalez on Unsplash, Salmon Photo by Casey Lee on Unsplash

Starting with a failing test

I want to use a TDD approach, so let’s start with a failing test. At this point, there is no component yet, so of course whatever test we write is going to fail. But let’s start small; I want a component named ‘Recipes’ that renders the expected heading text. Here is my test for that expectation:

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

	test('renders the heading', () => {
	  render(<Recipes />);

	  expect(screen.getByRole('heading')).toHaveTextContent('Recipe Finder');
	});

React testing library exports a render method, which will render a component and all of its child components. It also exports a screen object, holding a number of queries we can use to select different elements in our rendered component (and its child components too). The **getByRole **query lets me select the heading element and make an assertion on its text content.

Why select the heading element by its role and not for example a CSS class? The guiding principle of React Testing Library is “The more your tests resemble the way your software is used, the more confidence they can give you.” Therefore, we want to write our tests as close as possible to how the ultimate tester — the end user — will be using the application. Users don’t see CSS classes or data attributes; they interact with text, label text and semantic elements and roles. Using queries such as getByRole also encourages us to write accessible code, since these selectors are available to everyone, including users of screen readers.

Making the test pass

Our first test fails as expected.** Recipes is not defined.** But this is the first step in TDD — a failing test. Now, let’s make it pass by writing the simplest possible component with the correct heading and then importing it in our test file. Now, let’s re-run the test. It passes!

	import React from 'react';

	const Recipes = () => {
	  return (
	    <div>
	      <h1>Recipe Finder</h1>
	    </div>
	  )
	};

	export default Recipes;

Using further queries, we can make similar expectations for the input element and the “Find” button. The button also has a role, but for the input field, I will use the getByPlaceholderText query, since that is probably the closest query to how the user would find it on the page.

Start with a failing test…

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

	test('renders the heading, input field and button', () => {
	  render(<Recipes />);

	  expect(screen.getByRole('heading')).toHaveTextContent('Recipe Finder');
	  expect(screen.getByPlaceholderText('Enter an ingredient to find recipes...'))
	    .toBeInTheDocument();
	  expect(screen.getByRole('button')).toHaveTextContent('Find');
	});

… and implement the changes necessary to make it pass:

	import React from 'react';

	const Recipes = () => {
	  return (
	    <div>
	      <h1>Recipe Finder</h1>
	      <form>
	        <input 
	          type="text" 
	          name="ingredient"
	          placeholder="Enter an ingredient to find recipes..." 
	        />
	        <button type="submit">Find</button>
	      </form>
	    </div>
	  )
	};

	export default Recipes;

This way, we know what we expect from our code and more importantly — we will know if we break any functionality if the previously passing tests suddenly fail.

An important step in TDD is the refactor step, where we improve our code to for example make it easier to read, become more efficient and remove any duplication. The test should still pass after we refactor.

Setting up our mocks

When the application first renders, I want to display a list of all my recipes, just like in the visual design above. This requires some kind of communication with an API. We are going to use Mock Service Worker to mock the HTTP-requests, so that we can control the response data. Install Mock Service Worker with npm like this:

npm install msw --save-dev

With Mock Service Worker, we are not mocking a specific module (unlike if we were to use Jest.mock), which means that it makes no difference if I use fetch or a third-party library such as axios to get the data. This makes it incredibly flexible. Let’s add the following imports to our test file:

import { rest } from 'msw';
import { setupServer } from 'msw/node';

Here is how I set up mocking a call to the recipe list endpoint:

	import React from 'react';
	import { render, screen } from '@testing-library/react';
	import Recipes from './Recipes';
	import { rest } from 'msw';
	import { setupServer } from 'msw/node';

	const allRecipes = [
	  { id: 1, title: 'Burger' }, 
	  { id: 2, title: 'French toast' }, 
	  { id: 3, title: 'Salmon' }
	];

	const server = setupServer(
	  rest.get('/api/recipes', (req, res, ctx) => {
	    return res(ctx.json({ recipes: allRecipes }));
	  })
	);

	beforeAll(() => server.listen());

afterAll(() => server.close());

If you have worked with NodeJS and Express, the syntax looks very familiar. GET requests to ‘/api/recipes’ will respond with JSON containing the allRecipes array, just like a real API would. These two lines make sure the server starts listening (intercepting) before the tests run and closes its connection when the tests in this file have finished running:

beforeAll(() => server.listen());
afterAll(() => server.close());

#tdd #react-testing-library #react #test-driven-development #testing

Simulate Browser Interactions with Testing Library’s UserEvent

My Journey

Like most, when I first started using Testing Library, I used Fire Event to test component interactions. After all, this API shipped with the library itself and was used in the test examples in the documentation. But I soon discovered that Fire Event had serious limitations. I would try clicking something and the expected effect did not happen. Why?

Browser Events

To understand this issue, we need to better understand browser events. When a user clicks something in their browser, multiple events are triggered — mouseDown, mouseUp, click, and focus. Similarly, when typing something, the keyDown, keyUp, and keyPress events all trigger! Because a single user interaction could trigger multiple events, developers have multiple options for implementation. This is where I ran into my issue.

Fire Event

Fire Event, unfortunately, requires you to use the method for the corresponding event handler to trigger. If an element has an onClick event handler, I have to use fireEvent.click; if an element has an onMouseDown event handler, I have to use fireEvent.mouseDown. In other words, I need to know the exact implementation of the event handler to successfully use fireEvent.

#react #jest #integration-testing #unit-testing #react-testing-library #react native

How React Testing Library Can Improve Your Mental Health [Part 1]

I know one person who likes writing tests, and it is not me! I like adding code-coverage to my code and you’ll see why.

My name is Maciej, I’m a software engineer, and you can find how to pronounce my name here: sayoname.com/me/maciej

Omitting tests is OK only if the project is your small to-do app.

Not having tests will become a problem sooner or later. Now you might deploy features quickly. But the day when you cannot release for weeks because of cropping bugs here and there will come and this will happen…

If the project grows it WILL become a problem! Imagine - you start getting users, making money, hiring devs, there are so many feature going on that you will not be able to keep all those dependencies in your head.

I worked in a place once which had a pretty big code project with no tests at all. The repo was massive, thousands of customers used it every day and they paid millions. But customers were paying and they wanted new features. Some were simple, like changing text and adding a button here and there. Some were more complex like providing integration with external software.

One day we got our Product Owner (PO) who specified this new requirement. We needed a few new reports for customers, which were basically a couple of new tables. What started as a small task which we scoped around 4-weeks until production. Turned out to be a 4-month struggle with tens if not hundreds of bugs raised by QA.

Why was that? It wasn’t the technology used, it wasn’t the developers ;) and it wasn’t the complexity of the project. It was the lack of tests!

There were three of us working on those features, and due to no tests, we didn’t know if our changes break someone else’s code!

Another problem was that those bugs were usually found after a couple of days of full manual regression testing. After a bug was raised we had to pick bug fixes as a priority and switch context. And then investigate, trying to remember why I wrote this rubbish code, fix it, create a PR, get it approved, and then release (obviously manually, because what did you expect from a no tests codebase).

This massive gig made the business realize we cannot do it anymore and a decision has been made to rewrite the whole app! It took almost 18 months and obviously, no new features were added in the meantime.

You get now why tests are important. You don’t? Close the page, you’ll never get it! Get back to adding functionality and stop wasting your precious time even reading about tests!

#react #react-testing-library #reactjs #testing