Convert Enzyme wrappers to a format compatible with Jest snapshot testing.
$ npm install --save-dev enzyme-to-jsonimport React, { Component } from 'react';
import { shallow } from 'enzyme';
import toJson from 'enzyme-to-json';
class MyComponent extends Component {
constructor() {
super();
this.handleClick = this.handleClick.bind(this);
this.state = { count: 1 };
}
handleClick() {
this.setState(({ count }) => ({ count: count + 1 }));
}
render() {
return (
<div className={this.props.className} onClick={this.handleClick}>
<span className="count">{this.state.count}</span>
{this.props.children}
</div>
);
}
}
it('renders correctly', () => {
const wrapper = shallow(
<MyComponent className="my-component">
<strong>Hello World!</strong>
</MyComponent>
);
expect(toJson(wrapper)).toMatchSnapshot();
});
// generates:
exports[`test renders correctly 1`] = `
<div
className="my-component"
onClick={[Function]}>
<span
className="count">
1
</span>
<strong>
Hello World!
</strong>
</div>
`;It becomes especially handy as you can use all Enzyme features like find or setState:
it('renders span after setState', () => {
const wrapper = shallow(
<MyComponent className="my-component">
<strong>Hello World!</strong>
</MyComponent>
);
wrapper.setState({ count: 42 });
expect(toJson(wrapper.find('span'))).toMatchSnapshot();
});
// generates:
exports[`test renders span after setState 1`] = `
<span
className="count">
42
</span>
`;It could be useful if you want more focused tests.
This library also supports mount and render Enzyme wrappers:
it('mounts my component', () => {
const wrapper = mount(
<MyComponent className="my-component">
<strong>Hello World!</strong>
</MyComponent>
);
expect(toJson(wrapper)).toMatchSnapshot();
});
it('renders my component', () => {
const wrapper = render(
<MyComponent className="my-component">
<strong>Hello World!</strong>
</MyComponent>
);
expect(toJson(wrapper)).toMatchSnapshot();
});You can still use the shallowToJson, mountToJson and renderToJson wrappers from the earlier versions, importing them like this:
import {shallowToJson, mountToJson, renderToJson} from 'enzyme-to-json';
If you are using Jest v17.0.0 or higher, you can also use a Jest serializer.
Add this to your Jest configuration:
"snapshotSerializers": ["<rootDir>/node_modules/enzyme-to-json/serializer"]If you use Jest v18.0.0 or higher, you can use a shorthand:
"snapshotSerializers": ["enzyme-to-json/serializer"]Then you can use all of the above without having to include or use the toJson function! For example:
it('mounts my component', () => {
const wrapper = shallow(
<MyComponent className="my-component">
<strong>Hello World!</strong>
</MyComponent>
);
expect(wrapper).toMatchSnapshot();
});
it('mounts my component', () => {
const wrapper = mount(
<MyComponent className="my-component">
<strong>Hello World!</strong>
</MyComponent>
);
expect(wrapper).toMatchSnapshot();
});
it('renders my component', () => {
const wrapper = render(
<MyComponent className="my-component">
<strong>Hello World!</strong>
</MyComponent>
);
expect(wrapper).toMatchSnapshot();
});This is inspired by jest-serializer-enzyme, I first added a note to jest-serializer-enzyme but I then realised that the output is different, so it is not retro compatible with enzyme-to-json because it's using Enzyme debug helper which doesn't put each prop on a separate line.
For example the output of the first example would be:
exports[`test renders correctly 1`] = `
<div className="my-component" onClick={[Function]}>
<span className="count">
1
</span>
<strong>
Hello World!
</strong>
</div>
`;instead of:
exports[`test renders correctly 1`] = `
<div
className="my-component"
onClick={[Function]}>
<span
className="count">
1
</span>
<strong>
Hello World!
</strong>
</div>
`;which is different from ours. So, if you want to move from enzyme-to-json to jest-serializer-enzyme, you would have to update all snapshots.
The output is a matter of preference, also jest-serializer-enzyme only supports the shallow wrapper for now, so if you're already using enzyme-to-json, it's a bit easier to use our serializer for now. Thanks to @rogeliog for bringing up the idea.
One thing I really like about this library is the ability to use find and Enzyme selectors to have focused tests.
For example, with react-test-renderer (used in Jest documentation), you would test a component like that:
import React from 'react';
import renderer from 'react-test-renderer';
const MyComponent = props => (
<div className={`my-component ${props.className}`}>
<h3>Component Heading</h3>
<span>{props.children}</span>
</div>
);
it('renders a `strong` correctly', () => {
const wrapper = renderer.create(
<MyComponent className="strong-class">
<strong>Hello World!</strong>
</MyComponent>
);
expect(wrapper).toMatchSnapshot();
});
it('renders a `span` correctly', () => {
const wrapper = renderer.create(
<MyComponent className="span-class">
<span>Hello World!</span>
</MyComponent>
);
expect(wrapper).toMatchSnapshot();
});and so on, handling all test cases. The problem, is that when you decide to change Component Heading to Component Title, you will get a failing snapshot test for each test with a long output like that:
● renders a `strong` correctly
Received value does not match the stored snapshot 1.
- Snapshot
+ Received
<div
className="my-component strong-class">
<h3>
- Component Heading
+ Component Title
</h3>
<span>
<strong>
Hello World!
</strong>
</span>
</div>
at Object.<anonymous> (test/focused.test.js:22:21)
at process._tickCallback (internal/process/next_tick.js:103:7)
● renders a `span` correctly
Received value does not match the stored snapshot 1.
- Snapshot
+ Received
<div
className="my-component span-class">
<h3>
- Component Heading
+ Component Title
</h3>
<span>
<span>
Hello World!
</span>
</span>
</div>
at Object.<anonymous> (test/focused.test.js:32:21)
at process._tickCallback (internal/process/next_tick.js:103:7)and so on, you may have 10 or more snapshot tests for the same component to handle different test cases.
When using Enzyme find helper, you can write your tests focusing on a specific part of the output, like that:
import React from 'react';
import { shallow } from 'enzyme';
import toJson from 'enzyme-to-json';
const MyComponent = props => (
<div className={`my-component ${props.className}`}>
<h3>Component Heading</h3>
<span>{props.children}</span>
</div>
);
it('renders the right title', () => {
const wrapper = shallow(
<MyComponent className="strong-class"/>
);
expect(toJson(wrapper.find('h3'))).toMatchSnapshot();
});
it('renders a `strong` correctly', () => {
const wrapper = shallow(
<MyComponent className="strong-class">
<strong>Hello World!</strong>
</MyComponent>
);
expect(toJson(wrapper.find('span').first())).toMatchSnapshot();
});
it('renders a `span` correctly', () => {
const wrapper = shallow(
<MyComponent className="span-class">
<span>Hello World!</span>
</MyComponent>
);
expect(toJson(wrapper.find('span').first())).toMatchSnapshot();
});Testing that the component renders a span and a strong is in a different test from testing that the title is correct and they will only fail if the component doesn't render span or strong correctly. When the title changes, only the first snapshot test will fail:
● renders the right title
Received value does not match the stored snapshot 1.
- Snapshot
+ Received
<h3>
- Component Heading
+ Component Title
</h3>
at Object.<anonymous> (test/focused.test.js:19:93)
at process._tickCallback (internal/process/next_tick.js:103:7)See CONTRIBUTING.md.
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