Here's my lazy component:
const LazyBones = React.lazy(() => import('#graveyard/Bones')
.then(module => ({default: module.BonesComponent}))
export default LazyBones
I'm importing it like this:
import Bones from './LazyBones'
export default () => (
<Suspense fallback={<p>Loading bones</p>}>
<Bones />
</Suspense>
)
And in my test I have this kind of thing:
import * as LazyBones from './LazyBones';
describe('<BoneYard />', function() {
let Bones;
let wrapper;
beforeEach(function() {
Bones = sinon.stub(LazyBones, 'default');
Bones.returns(() => (<div />));
wrapper = shallow(<BoneYard />);
});
afterEach(function() {
Bones.restore();
});
it('renders bones', function() {
console.log(wrapper)
expect(wrapper.exists(Bones)).to.equal(true);
})
})
What I expect is for the test to pass, and the console.log to print out:
<Suspense fallback={{...}}>
<Bones />
</Suspense>
But instead of <Bones /> I get <lazy /> and it fails the test.
How can I mock out the imported Lazy React component, so that my simplistic test passes?
I'm not sure this is the answer you're looking for, but it sounds like part of the problem is shallow. According to this thread, shallow won't work with React.lazy.
However, mount also doesn't work when trying to stub a lazy component - if you debug the DOM output (with console.log(wrapper.debug())) you can see that Bones is in the DOM, but it's the real (non-stubbed-out) version.
The good news: if you're only trying to check that Bones exists, you don't have to mock out the component at all! This test passes:
import { Bones } from "./Bones";
import BoneYard from "./app";
describe("<BoneYard />", function() {
it("renders bones", function() {
const wrapper = mount(<BoneYard />);
console.log(wrapper.debug());
expect(wrapper.exists(Bones)).to.equal(true);
wrapper.unmount();
});
});
If you do need to mock the component for a different reason, jest will let you do that, but it sounds like you're trying to avoid jest. This thread discusses some other options in the context of jest (e.g.
mocking Suspense and lazy) which may also work with sinon.
You don't need to resolve lazy() function by using .then(x => x.default) React already does that for you.
React.lazy takes a function that must call a dynamic import(). This must return a Promise which resolves to a module with a default export containing a React component. React code splitting
Syntax should look something like:
const LazyBones = React.lazy(() => import("./LazyBones"))
Example:
// LazyComponent.js
import React from 'react'
export default () => (
<div>
<h1>I'm Lazy</h1>
<p>This component is Lazy</p>
</div>
)
// App.js
import React, { lazy, Suspense } from 'react'
// This will import && resolve LazyComponent.js that located in same path
const LazyComponent = lazy(() => import('./LazyComponent'))
// The lazy component should be rendered inside a Suspense component
function App() {
return (
<div className="App">
<Suspense fallback={<p>Loading...</p>}>
<LazyComponent />
</Suspense>
</div>
)
}
As for Testing, you can follow the React testing example that shipped by default within create-react-app and change it a little bit.
Create a new file called LazyComponent.test.js and add:
// LazyComponent.test.js
import React, { lazy, Suspense } from 'react'
import { render, screen } from '#testing-library/react'
const LazyComponent = lazy(() => import('./LazyComponent'))
test('renders lazy component', async () => {
// Will render the lazy component
render(
<Suspense fallback={<p>Loading...</p>}>
<LazyComponent />
</Suspense>
)
// Match text inside it
const textToMatch = await screen.findByText(/I'm Lazy/i)
expect(textToMatch).toBeInTheDocument()
})
Live Example: Click on the Tests Tab just next to Browser tab. if it doesn't work, just reload the page.
You can find more react-testing-library complex examples at their Docs website.
I needed to test my lazy component using Enzyme. Following approach worked for me to test on component loading completion:
const myComponent = React.lazy(() =>
import('#material-ui/icons')
.then(module => ({
default: module.KeyboardArrowRight
})
)
);
Test Code ->
//mock actual component inside suspense
jest.mock("#material-ui/icons", () => {
return {
KeyboardArrowRight: () => "KeyboardArrowRight",
}
});
const lazyComponent = mount(<Suspense fallback={<div>Loading...</div>}>
{<myComponent>}
</Suspense>);
const componentToTestLoaded = await componentToTest.type._result; // to get actual component in suspense
expect(componentToTestLoaded.text())`.toEqual("KeyboardArrowRight");
This is hacky but working well for Enzyme library.
To mock you lazy component first think is to transform the test to asynchronous and wait till component exist like:
import CustomComponent, { Bones } from './Components';
it('renders bones', async () => {
const wrapper = mount(<Suspense fallback={<p>Loading...</p>}>
<CustomComponent />
</Suspense>
await Bones;
expect(wrapper.exists(Bones)).toBeTruthy();
}
Related
I have a very simple class based component. Which looks like the following:
class MyComponent extends React.Component {
onPressButton () {
console.warn('button pressed')
const { contextFunction } = this.context
contextFunction()
}
render () {
return (
<div>
My Component
<button onClick={() => onPressButton()}>Press button</button>
</div>
)
}
}
MyComponent.contextType = SomeContext
That is all fine and well and works as expected. However, I am having trouble adding unit tests with jest and enzyme. My current code looks as follows:
test('should render test Press button', async () => {
const contextFunctionMock = jest.fn()
const wrapper = shallow(<MyComponent {...props} />)
wrapper.instance().context = { contextFunction: contextFunctionMock }
console.log('wrapper.instance()', wrapper.instance())
await wrapper.instance().onPressButton() // this works just fine
expect(contextFunctionMock).toHaveBeenCalled() // this errors, basically because ti complains contextFunction is not a function
})
As you can see above, I console.logged my wrapper.instance() to see what is going on.
Interestingly enough, the context on the root of the instance object is indeed what I expected it to be based on setting the context, which is something like:
context: {
contextFunction: [Function: mockConstructor] {
_isMockFunction: true,
getMockImplementation: [Function (anonymous)],
[...Other mock function properties]
}
...
However, there is a second context, which is in the updater property of the wrapper.instance(), and it is an empty object. Basically looks like the following:
updater: <ref *2> Updater {
_renderer: ReactShallowRenderer {
_context: {},
...
}
Not exactly sure if this is the context being used for my component's unit test, but it is currently just an empty object, which makes me think this may be the one being used for it.
Anyway, how can I properly mock my context functions to run on this particular unit tests? Also, why is this happening but does not happen in others with a similar set of circumstances?
Problem
A fundamental problem with your code above is that there's no way to assert that the context function is successfully/failing to be called. Right now, you're clicking a button, but there isn't any indication on what's happening after the button is clicked (nothing is being changed/updated within the context/component to reflect any sort of UI change). So asserting that a contextual function is called won't be beneficial if there's no result of clicking the button.
In addition to the above, the enzyme-adapter doesn't support context that uses the createContext method.
However, there's a work-around for this limitation! Instead of unit testing the component, you'll want to create an integration test with the context. Instead of asserting that a contextual function was called, you'll make assertions against the result of clicking on the button that changes context and how it affects the component.
Solution
Since the component is tied to what's in context, you'll create an integration test. For example, you'll wrap the component with context in your test and make assertions against the result:
import * as React from "react";
import { mount } from "enzyme";
import Component from "./path/to/Component";
import ContextProvider from "./path/to/ContextProvider";
const wrapper = mount(
<ContextProvider>
<Component />
</ContextProvider>
);
it("updates the UI when the button is clicked", () => {
wrapper.find("button").simulate("click");
expect(wrapper.find(...)).toEqual(...);
})
By doing the above, you can make assertions against contextual updates within the Component. In addition, by using mount, you won't have to dive into the ContextProvider to view the Component markup.
Demo Example
This demo utilizes context to toggle a theme from "light" to "dark" and vice versa. Click on the Tests tab to run the App.test.js integration test.
Code Example
App.js
import * as React from "react";
import { ThemeContext } from "./ThemeProvider";
import "./styles.css";
class App extends React.PureComponent {
render() {
const { theme, toggleTheme } = this.context;
return (
<div className="app">
<h1>Current Theme</h1>
<h2 data-testid="theme" className={`${theme}-text`}>
{theme}
</h2>
<button
className={`${theme}-button button`}
data-testid="change-theme-button"
type="button"
onClick={toggleTheme}
>
Change Theme
</button>
</div>
);
}
}
App.contextType = ThemeContext;
export default App;
ThemeProvider.js
import * as React from "react";
export const ThemeContext = React.createContext();
class ThemeProvider extends React.Component {
state = {
theme: "light"
};
toggleTheme = () => {
this.setState((prevState) => ({
theme: prevState.theme === "light" ? "dark" : "light"
}));
};
render = () => (
<ThemeContext.Provider
value={{ theme: this.state.theme, toggleTheme: this.toggleTheme }}
>
{this.props.children}
</ThemeContext.Provider>
);
}
export default ThemeProvider;
index.js
import * as React from "react";
import ReactDOM from "react-dom";
import ThemeProvider from "./ThemeProvider";
import App from "./App";
ReactDOM.render(
<React.StrictMode>
<ThemeProvider>
<App />
</ThemeProvider>
</React.StrictMode>,
document.getElementById("root")
);
Test Example
An example of how to test against the demo example above.
withTheme.js (an optional reusable testing factory function to wrap a component with context -- especially useful for when you may want to call wrapper.setProps() on the root to update a component's props)
import * as React from "react";
import { mount } from "enzyme";
import ThemeProvider from "./ThemeProvider";
/**
* Factory function to create a mounted wrapper with context for a React component
*
* #param Component - Component to be mounted
* #param options - Optional options for enzyme's mount function.
* #function createElement - Creates a wrapper around passed in component with incoming props (now we can use wrapper.setProps on root)
* #returns ReactWrapper - a mounted React component with context.
*/
export const withTheme = (Component, options = {}) =>
mount(
React.createElement((props) => (
<ThemeProvider>{React.cloneElement(Component, props)}</ThemeProvider>
)),
options
);
export default withTheme;
App.test.js
import * as React from "react";
import { configure } from "enzyme";
import Adapter from "enzyme-adapter-react-16";
import withTheme from "./withTheme";
import App from "./App";
configure({ adapter: new Adapter() });
// wrapping "App" with some context
const wrapper = withTheme(<App />);
/*
THIS "findByTestId" FUNCTION IS OPTIONAL!
I'm using "data-testid" attributes, since they're static properties in
the DOM that are easier to find within a "wrapper".
This is 100% optional, but easier to use when a "className" may be
dynamic -- such as when using css modules that create dynamic class names.
*/
const findByTestId = (id) => wrapper.find(`[data-testid='${id}']`);
describe("App", () => {
it("initially displays a light theme", () => {
expect(findByTestId("theme").text()).toEqual("light");
expect(findByTestId("theme").prop("className")).toEqual("light-text");
expect(findByTestId("change-theme-button").prop("className")).toContain(
"light-button"
);
});
it("clicking on the 'Change Theme' button toggles the theme between 'light' and 'dark'", () => {
// change theme to "dark"
findByTestId("change-theme-button").simulate("click");
expect(findByTestId("theme").text()).toEqual("dark");
expect(findByTestId("theme").prop("className")).toEqual("dark-text");
expect(findByTestId("change-theme-button").prop("className")).toContain(
"dark-button"
);
// change theme to "light"
findByTestId("change-theme-button").simulate("click");
expect(findByTestId("theme").text()).toEqual("light");
});
});
As for today, the new context API is not supported by enzyme, the only solution I found is to use this utility https://www.npmjs.com/package/shallow-with-context
import { configure, shallow } from "enzyme";
import Adapter from "enzyme-adapter-react-16";
import { withContext } from "shallow-with-context";
import MyComponent from "./MyComponent";
configure({ adapter: new Adapter() });
describe("Context", () => {
it("should render test Press button", async () => {
const contextFunctionMock = jest.fn();
const context = { contextFunction: contextFunctionMock };
const MyComponentWithContext = withContext(MyComponent, context);
const wrapper = shallow(<MyComponentWithContext />, { context });
await wrapper.instance().onPressButton();
expect(contextFunctionMock).toHaveBeenCalled();
});
});
https://codesandbox.io/s/enzyme-context-test-xhfj3?file=/src/MyComponent.test.tsx
This is a Lazy Route component I wrote a while ago (code below).
This is what it does:
It initially render a lazyLoading = true state to show some spinner or something.
Then on useEffect it will dynamic import() a component module and set the LazyComponent state. Like setLazyComponent(module)
Then it will turn the loading to false and render <LazyComponent.default />
Note: It works as intended.
My question is:
I've tried to do the following:
Set the default property to the state. As in setLazyComponent(module.default). Since SomeComponent, which is the component that is being lazy loaded has a single default export.
Then I should be able to render just <LazyComponent/> instead of <LazyComponent.default/>
But it does not work.
And I get this error:
Why does it not work? All the rest of the code is the same. The only change I'm trying to make is the place where I access the default property.
import React, { useEffect, useState } from 'react';
import styled from 'styled-components';
const LS = {};
LS.Container_DIV = styled.div`
`;
async function lazyRender() {
const module = await import("./SomeComponent");
return new Promise((resolve) => {
resolve(module);
});
}
function LazyRoute(props) {
console.log('Rendering LazyRoute...');
const [lazyLoading,setLazyLoading] = useState(true);
const [LazyComponent,setLazyComponent] = useState(null);
useEffect(() => {
async function getLazyComponent() {
const module = await lazyRender();
setLazyComponent(module);
setLazyLoading(false);
}
getLazyComponent();
},[]);
return(
lazyLoading ?
<div>I am Lazy Loading....</div>
: <LazyComponent.default {...props}/>
);
}
export default React.memo(LazyRoute);
How would I be able to test the router in the code below? When using React you are able to use MemoryRouter to pass initialEntries to mock a route change but I cannot find an alternative for preact-router. I looked at the Preact docs and the preact-router docs but I am unable to find a clear solution.
import 'preact/debug';
import { h, render } from 'preact';
import HomePage from './pages/homepage';
import Router from 'preact-router';
import AsyncRoute from 'preact-async-route';
import './styles/index.scss';
const App = () => (
<Router>
<HomePage path="/" />
<AsyncRoute
path="/admin"
getComponent={ () => import('./pages/admin').then(module => module.default) }
/>
</Router>
);
export default App;
This is a little old, but I figured I would share what I found.
The first and quickest thing to do is to just use the route function in preact-router.
import { render, route } from 'preact-router';
import App from './App';
describe('<App/>', () => {
it('renders admin', async () => {
const { container, findByText } = render(<App/>);
// Go to admin page
route('/admin');
// Wait for page to load since it's loaded async
await findByText(/Admin Page/);
// perform expectations.
});
});
While this works, I don't like that it relies on the brower's real history. Luckily, the <Router> component accepts a history prop of type CustomHistory. So you can use an in-memory implementation of a History API to make this happen. I think I've seen docs that suggest using the history package - however I had to make an adjustment
import { createMemoryHistory } from 'history';
class MemoryCustomHistory {
constructor(initialEntries = undefined) {
this.wrapped = createMemoryHistory({initialEntries});
}
get location() {
return this.wrapped.location;
}
// Listen APIs not quite compatible out of the box.
listen(callback) {
return this.wrapped.listen((locState) => callback(locState.location));
}
push(path) {
this.wrapped.push(path);
}
replace(path) {
this.wrapped.replace(path);
}
}
Next, update your app to accept a history property to pass to the <Router>
const App = ({history = undefined} = {}) => (
<Router history={history}>
<HomePage path="/" />
<AsyncRoute
path="/admin"
getComponent={ () => import('./pages/admin').then(module => module.default) }
/>
</Router>
);
Finally, just update the tests to wire your custom history to the app.
it('renders admin', async () => {
const history = new MemoryCustomHistory(['/admin]);
const { container, findByText } = render(<App history={history}/>);
// Wait for page to load since it's loaded async
await findByText(/Admin Page/);
// perform expectations.
});
I'm having trouble testing my React components that use react-loadable. Say, I have a Button component that, depending on whether it receives an icon prop, loads an Icon component like so:
Button.js
const LoadableIcon = Loadable({
loader: () => import('./Icon'),
loading: () => <div>Loading...</div>
})
function Button(props) {
return (
<button
onClick={props.onClick}>
{props.icon &&
<LoadableIcon name={props.icon} />}
{props.children}
</button>
)
}
When I test this component, however, the Icon had not loaded yet, and instead the test only finds the <div>Loading...</div> element...
Button.test.js
import React from 'react'
import {render} from 'react-testing-library'
import Button from '../Button'
describe('Button', () => {
it('renders icon correctly', () => {
const {getByText} = render(
<Button
icon='add'
/>
)
expect(getByText('add')).toBeInTheDocument()
})
})
Is there an elegant way to handle this situation without using actual setTimeouts?
So, the answer is to read the docs - note to self! The solution based on docs was the following:
describe('Button', () => {
it('renders icon correctly', async () => {
const {getByText} = render(
<Button
icon='add'
/>
)
const icon = await waitForElement(() => getByText('add'))
expect(icon).toBeInTheDocument()
})
})
Also, note that async needs to be used together with await.
I don't have personal experience using react-loadable, but I have implemented a similar component that handles code splitting via the dynamic import() syntax.
To get Jest to work with 'loadable' / 'async' components, I had to configure my .babel-rc config for Jest to include the dynamic-import-node babel plugin that way the modules can be properly resolved even when the import is async.
I'm trying to test a simple component that take some props (it have no state, or redux connection) with Enzyme, it works for the plain elements like <div /> and so on, but when i try to test if the element rendered by the child component exists, it fails.
I'm trying to use mount but it spit me a lot of errors, i'm new in this so, here is my code:
import React, { Component } from 'react';
import WordCloud from 'react-d3-cloud';
class PredictWordCloud extends Component {
render() {
const fontSizeMapper = word => Math.log2(word.value) * 3.3;
const { size, data, show } = this.props;
if (!show)
return <h3 className='text-muted text-center'>No data</h3>
return (
<section id='predict-word-cloud'>
<div className='text-center'>
<WordCloud
data={data}
fontSizeMapper={fontSizeMapper}
width={size}
height={300} />
</div>
</section>
)
}
}
export default PredictWordCloud;
It's just a wrapper for <WordCloud />, and it just recieves 3 props directly from his parent: <PredictWordCloud data={wordcloud} size={cloudSize} show={wordcloud ? true : false} />, anything else.
The tests is very very simple for now:
import React from 'react';
import { shallow } from 'enzyme';
import PredictWordCloud from '../../components/PredictWordCloud.component';
import cloudData from '../../helpers/cloudData.json';
describe('<PredictWordCloud />', () => {
let wrapper;
beforeEach(() => {
wrapper = shallow(<PredictWordCloud data={cloudData} size={600} show={true} />)
});
it('Render without problems', () => {
const selector = wrapper.find('#predict-word-cloud');
expect(selector.exists()).toBeTruthy();
});
});
For now it pass but if we change the selector to: const selector = wrapper.find('#predict-word-cloud svg'); where the svg tag is the return of <Wordcloud /> component, the tests fails because the assertion returns false.
I tried to use mount instead of shallow, exactly the same test, but i get a big error fomr react-d3-cloud:
PredictWordCloud Render without problems TypeError: Cannot read property 'getImageData' of null.
This is specially weird because it just happens in the test environment, the UI and all behaviors works perfectly in the browser.
You can find your component directly by Component name.
Then you can use find inside your sub-component as well.
e.g
it('Render without problems', () => {
const selector = wrapper.find('WordCloud').first();
expect(selector.find('svg')).to.have.length(1);
});
or
You can compare generated html structure as well via
it('Render without problems', () => {
const selector = wrapper.find('WordCloud').first();
expect(selector.html()).to.equal('<svg> Just an example </svg>');
});