“Always code as if the guy who ends up maintaining your code will be a violent psychopath who knows where you live.” (Martin Golding)
Live Example: Codesandbox
I’ve always been curious about how testing works in React and how to get used to the habit of writing tests. So, finally gathered my courage and started my journey to testing in React. In my first attempt I came across with this incredible article written by Kent C. Dodds Introducing The React Testing Library The article was super insightful and has given me some direction to go, then I skim through lots of other articles about React Testing Library, and in the end, I had enough knowledge to make my own toy project.
Before we dive into React Testing Library, let’s first talk about “What Is Testing”.
Testing
Testing is one of the crucial parts of the software development process and mostly overlooked by developers. Usually, developers avoid writing tests, because it takes more time than just simply developing a product, if you are not familiar with tests. But there is only one way to make sure your code works as you keep working on it. Imagine a scenario where you develop a new component that works with your old component, you might be somehow modified your components, so how do you make sure your old component is working as you expected?. You can’t if you avoid writing tests. Period.
So, few gotchas:
- Write test and write them early
- Write your tests first
- Write tests that resemble the way your software is used
React Testing Library
RTL(React Testing Library) created to test our React components, and unlike other alternatives like Enzyme RTL is very intuitive and simple. Even, its setup is simple and ships with CRA(Create React App).
Let’s get started.
To start a new project with Typescript, run one of the following command.
npx create-react-app testing-with-chuck --template typescript
# or
yarn create react-app testing-with-chuck --template typescript
And, add following dependencies.
yarn add @chakra-ui/react @emotion/react @emotion/styled framer-motion axios ts-jest
We’ll use Chakra UI for styling, axios for API requets and ts-jest for mocking jest.
Project Structures
src -->
|-->__tests__
| |--> Home.spec.tsx
| |--> jokeApi.spec.tsx
|-->components
| |--> Home.tsx
|-->fixtures
| |--> Joke.ts
|-->services
| |--> jokeApi.ts
|-->App.tsx
|-->react-app-env.d.ts
I’ll not explain how React works, just provide some sample code to focus on testing.
App.tsx
import { ChakraProvider } from "@chakra-ui/react";
import React from "react";
import Home from "./components/Home";
function App() {
return (
<ChakraProvider>
<Home />
</ChakraProvider>
);
}
export default App;
Components
Home.tsx
import React, { useState, useEffect } from "react";
import { Box, Button, Flex, Skeleton, Text } from "@chakra-ui/react";
import { getARandomJoke } from "../services/jokeApi";
type ApiType = {
categories: [];
created_at: Date;
id: string;
updated_at: Date;
value: string;
};
const Home = () => {
const [joke, setJoke] = useState<ApiType>();
const [loading, setLoading] = useState(false);
const getARandom = async () => {
setLoading(true);
const data = await getARandomJoke();
setLoading(false);
return data;
};
const handleRefresh = async () => {
const joke = await getARandomJoke();
setJoke(joke);
};
useEffect(() => {
getARandom().then(response => setJoke(response));
}, []);
return (
<Flex
justify="center"
alignItems="center"
height="100vh"
backgroundColor="#fff4da"
data-testid="jokeContainer"
>
<Box d="flex" flexDirection={["column", "row"]} padding="1.2rem">
<Skeleton
isLoaded={!loading}
startColor="#000"
endColor="#fff4da"
height="40px"
marginX="1rem"
>
<Text
maxWidth="800px"
as="p"
alignSelf="center"
fontSize="1.5rem"
marginRight="1rem"
textDecoration="underline"
data-testid="jokeText"
>
{joke?.value}
</Text>
</Skeleton>
<Button
marginTop={["1.5rem", 0, 0, 0]}
alignSelf="center"
variant="outline"
fontSize="1rem"
onClick={() => handleRefresh()}
disabled={loading}
borderColor="#2a2c2e"
borderRadius="0"
_hover={{ backgroundColor: "#e8daba" }}
>
Refresh
</Button>
</Box>
</Flex>
);
};
export default Home;
Fixtures
Point of defining our fixtures is we want to simulate Axios response since we don’t have the luxury of requesting to API every time our tests run. Let’s define our fixtures.
Joke.ts
import { ApiType } from "../services/jokeApi";
export const singularJoke: ApiType = {
value: "Chuck Norris invented the internet so people could talk about how great Chuck Norris is.",
categories: [],
created_at: new Date(),
id: "1212",
updated_at: new Date(),
};
export const emptySingularStory: ApiType = {
value: "",
categories: [],
created_at: new Date(),
id: "1212",
updated_at: new Date(),
};
Services
jokeApi.ts
import axios from "axios";
const URI = "https://api.chucknorris.io/jokes/random";
export type ApiType = {
categories: [];
created_at: Date;
id: string;
updated_at: Date;
value: string;
};
export const getARandomJoke = async () => {
const { data } = await axios.get<ApiType>(URI);
return data;
};
Looks like, we are ready. Let’s start writing our first test.
Tests
Home.spec.tsx
import React from "react";
import Home from "../components/Home";
import { render, cleanup, waitFor, act, screen } from "@testing-library/react";
import "@testing-library/jest-dom";
import { singularJoke, emptySingularStory } from "../fixtures/Joke";
import { getARandomJoke } from "../services/jokeApi";
import { mocked } from "ts-jest/utils";
afterEach(() => {
cleanup;
jest.resetAllMocks();
});
jest.mock("../services/jokeApi");
const mockedAxios = mocked(getARandomJoke);
test("Renders home correctly", async () => {
await act(async () => {
const { getByTestId } = render(<Home />);
expect(getByTestId("jokeContainer")).toBeInTheDocument();
});
});
test("Renders a joke correctly", async () => {
mockedAxios.mockImplementationOnce(() => Promise.resolve(singularJoke));
await act(async () => {
const { getByText } = render(<Home />);
await waitFor(() => [
expect(
getByText(
"Chuck Norris invented the internet so people could talk about how great Chuck Norris is."
)
).toBeTruthy(),
]);
});
});
test("Renders empty a joke correctly", async () => {
mockedAxios.mockImplementationOnce(() => Promise.resolve(emptySingularStory));
await act(async () => {
render(<Home />);
await waitFor(() => [expect(screen.getByTestId("jokeText")).toHaveTextContent("")]);
});
});
Before we start writing our test cases, we should first think about which functionalities we want to test.
- We want our Home component getting rendered correctly in the DOM.
- We want our Home component getting rendered with Chuck Norris joke and without a joke
Quick Note:
We need to give data-testid to elements we want to test to query and locate them in the DOM. If you scroll up, you will see that we’ve given jokeContainer to Home components div and jokeText to Text component renders our Chuck Norris Joke.
Let’s go through line by line:
afterEach => After each test case this function cleans the DOM and reset all mocks, so in the next test we don’t have to deal with older versions of DOM or mocks.
jest.mock('../services/jokeApi'); => In order to mock our Axios requests, we import it this way.
mocked(getARandomJoke) => With the help of ts-jest, we mock our Axios function to call it inside test cases.
test() => Test method receives name and callback function
act() => If your code contains useState(),useEffect() or any other code that updates your components use act().
const { getByTestId } = render(<Home />) => We tell to our Home component that we want to query it by testid.
expect(getByTestId('jokeContainer')).toBeInTheDocument(); => This is actually self explanatory, we tell that we expect Element with jokeContainer id to be in the document.
If we type yarn test now, you will see that PASS src/__tests__/home.spec.tsx.
Let’s move on to the second case.
mockedAxios.mockImplementationOnce(()
=> Promise.resolve(singularJoke)); => We call method called mockImplementationOnce() to mock a request, and tell it to return a single joke.
const { getByText } = render(<Home />); => Like getByTestId we can also query by text using getByText.
waitFor() => If we are having async requests inside our component we should use waitFor() to await a promise.
toBeTruthy() => Since, our singularJoke contains joke exactly like this Chuck Norris invented the internet so people could talk about how great Chuck Norris is.,
and we know this is truthy and we want to ensure a value is true in a boolean context.
Let’s move to our the third case.
mockedAxios.mockImplementationOnce(()
=> Promise.resolve(emptySingularStory)); => We want to test empty joke case.
Only difference between our second and third test case is toHaveTextContent. Since, we want to check given element has a text content or not,
and since we don’t have any text inside jokeText toHaveTextContent will fulfill our test case.
Testing Axios requests in isolation
import { singularJoke, emptySingularStory } from "../fixtures/Joke";
import { getARandomJoke } from "../services/jokeApi";
import axios from "axios";
jest.mock("axios");
const mockedAxios = axios as jest.Mocked<typeof axios>;
describe("Chuck Norris Api", () => {
beforeEach(() => {
jest.resetAllMocks();
});
describe("getStory functionality", () => {
it("requests and gets a joke from the chuckNorris Api", async () => {
mockedAxios.get.mockImplementation(() => Promise.resolve({ data: singularJoke }));
const entity = await getARandomJoke();
expect(axios.get).toHaveBeenCalledTimes(1);
expect(entity).toEqual(singularJoke);
});
it("does not retrieve a joke from the Api", async () => {
mockedAxios.get.mockImplementation(() => Promise.resolve({ data: emptySingularStory }));
const entity = await getARandomJoke();
expect(axios.get).toHaveBeenCalledTimes(1);
expect(entity).toEqual(emptySingularStory);
});
});
});
As can be seen, we have two test cases. Our first test case is to call the API and make sure it returns a joke. Second test case is also similar, but make sure API does not return a joke.
Final Thoughts
Tests matters, because it makes our code future proof to incoming changes, refactorings. So, write tests for things that might break in the future. Don’t write tests for everything.