react-component-driver

* React Component Driver

** About

Think about this package as friendly guide to help you black-box test React
components. It evolved from real world experience writing applications in
Angular, React, and React Native. It's a collection of best practices converted
to a thin layer of utility functions.

** Overview

* Rendering to JSON

Main concept that all utilities are built on is simple JSON tree derived (rendered) from React elements. At the core we have functions =render= and =toJSON=.

#+BEGIN_SRC js
const assert = require('assert');
const {render, toJSON} = require('react-component-driver');

const json = toJSON(render(Wix));

assert.deepEqual(json, { type: 'a', props: { href: 'wix.com' }, children: [ 'Wix' ] });
#+END_SRC

There is also a =renderComponent= helper which accepts component class or function and props.

#+BEGIN_SRC js
function Link({href, text}) {
return {text};
}

const json = toJSON(renderComponent(Link, {href: 'wix.com', text: 'Wix'}));

assert.deepEqual(json, { type: 'a', props: { href: 'wix.com' }, children: [ 'Wix' ] });
#+END_SRC

* Querying

To improve on snapshot testing we need to be able to assert on parts of component tree. There are multiple utilities that allow to filter JSON tree nodes.

Most general is =filterBy=.

#+BEGIN_SRC js
function Links({hrefs}) {
return

{hrefs.map(([href, text]) =>
• {text}
)}

;
}

const json = toJSON(renderComponent(Links, {hrefs: [
['wix.com', 'Wix'], ['deviantart.com', 'DeviantArt'], ['flok.com', 'Flok']
]}));

const result = filterBy((node) => node.props && node.props.href === 'wix.com', json);

assert.deepEqual(result, [{ type: 'a', props: { href: 'wix.com' }, children: [ 'wix.com' ] }]);
#+END_SRC

Be aware that nodes that =filterBy= passes to filtering predicate can be =null= or of =string= type besides full nodes with type, props and children.

Two more filtering functions are available out of the box. Both of them based on =filterBy= -- =filterByTestID= and =filterByType=.

=filterByTestID= can find nodes that have prop =testID= (React Native) or =data-test-id= (React on Web) matching exact value or regular expression.

#+BEGIN_SRC js
filterByTestID('exact-test-id', tree);
filterByTestID(/^list-item-[0-9]+$/, tree);
#+END_SRC

=filterByType= does exactly what you think -- filters by =type= field.

#+BEGIN_SRC js
filterByType('a', tree);
#+END_SRC

There is also another predefined helper =getTextNodes=. It allows to extract all text leaves.

#+BEGIN_SRC js

const json = toJSON(renderComponent(Links, {hrefs: [
['wix.com', 'Wix'], ['deviantart.com', 'DeviantArt'], ['flok.com', 'Flok']
]}));

const strings = getTextNodes(json);

assert.deepEqual(strings, [ 'Wix', 'DeviantArt', 'Flok' ]);
#+END_SRC

* Abstraction using Component Driver

It is beneficial to abstract queries as functions with descriptive names. Let's revisit example from before:

#+BEGIN_SRC js
function Links({hrefs}) {
return

{hrefs.map(([href, text]) =>
• {text}
)}

;
}

const json = toJSON(renderComponent(Links, {hrefs: [
['wix.com', 'Wix'], ['deviantart.com', 'DeviantArt'], ['flok.com', 'Flok']
]}));

const result = filterBy((node) => node.props && node.props.href === 'wix.com', json);

assert.ok(!!result[0], 'Has wix.com link.');
#+END_SRC

=ComponentDriver= can help make intention of above code clearer.

#+BEGIN_SRC js
const {ComponentDriver} = require('react-component-driver');

class LinksDriver extends ComponentDriver {
constructor() {
super(Links);
}
hasWixLink() {
return !!this.getBy((node) => node.props && node.props.href === 'wix.com');
}
}

const hrefs = [['wix.com', 'Wix'], ['deviantart.com', 'DeviantArt'], ['flok.com', 'Flok']];

assert.ok(new LinksDriver().setProps({hrefs}).hasWixLink(), 'Has wix.com link.');
#+END_SRC

There is also a function interface if you prefer.

#+BEGIN_SRC js
const {componentDriver} = require('react-component-driver');

function links() {
return componentDriver(Links, {
hasWixLink() {
return !!this.getBy((node) => node.props && node.props.href === 'wix.com');
}
});
}

assert.ok(links().setProps({hrefs}).hasWixLink(), 'Has wix.com link.');
#+END_SRC

=ComponentDriver= exposes methods similar to the ones described in Querying section. These methods are =filterBy=, =filterByType=, =filterByID=. There are also corresponding methods that return first matched node -- =getBy=, =getByType=, =getByID=. In addition, there is =getComponent= to retrieve root node, =render= -- to invoke =getComponent=, i.e. start React life-cycle, but discard result. =unmount= to initiate unmounting. To set props for rendering, use =setProps=. It's possible to attach driver to pre-rendered tree or sub-tree by using =attachTo= method.

Let's study example below to see example usages of =ComponentDriver= API.

** Example Component: List of Links

We are going to define to components -- a link and a list of links.

#+BEGIN_SRC js
class Link extends React.PureComponent {
onPress = () => this.props.onPress(this.props.url);
render() {
return (

{this.props.title}

);
}
}
#+END_SRC

=List= component depends on React Native =Linking= service and we make it clear by we declaring it as parameter. This will allow use to write tests and not depend on side effects.

#+BEGIN_SRC js
const links = (Linking) => class Links extends React.PureComponent {
keyExtractor = (link) => link.url;
renderLink = (data) => ;
onLinkPress = (url) => Linking.openURL(url);
render() {
return (
extractKey={this.keyExtractor}
data={this.props.links}
renderItem={this.renderLink}
/>
);
}
};
#+END_SRC

** Link Test Driver

#+BEGIN_SRC js
class LinkDriver extends ComponentDriver {
constructor() {
super(Link);
}
getTitle() {
return getTextNodes(this.getComponent()).join('');
}
tap() {
this.getComponent().props.onPress();
}
}
#+END_SRC

** Links Test Driver

Here you can find example of =attachTo=. Reusing =LinkDriver= removes dependency on concrete =Link= implementation.

#+BEGIN_SRC js
class LinksDriver extends ComponentDriver {
constructor(Linking) {
super(links(Linking));
}
getLinks() {
return this.filterByID(/^link-[0-9]+$/)
.map(link => new LinkDriver().attachTo(link));
}
getLinkTitles() {
return this.getLinks().map(link => link.getTitle());
}
tapLink(title) {
for (const link of this.getLinks()) {
if (link.getTitle() === title) {
link.tap();
break;
}
}
return this;
}
}
#+END_SRC

** Integration Tests

=Link= tests are relatively simple as it's pure component and behaviour depends completely on what is passed via props.

#+BEGIN_SRC js
describe('Link', () => {
it('should render title', () => {
const drv = new LinkDriver().setProps({title: 'A Link'});
expect(drv.getTitle()).to.equal('A Link');
});

it('should open URL on press', () => {
const onPress = sinon.spy();
new LinkDriver()
.setProps({url: 'wix://contacts/contact/123', onPress})
.tap();
expect(onPress).to.be.calledWith('wix://contacts/contact/123');
});
});
#+END_SRC

=Links= is a lot more interesting. It depends on a =Linking= service which has side-effects. Moreover, =LinksDriver= uses =LinkDriver= to query and control embedded =Link= components.

#+BEGIN_SRC js
describe('Links', () => {
const links = [{url: 'wix://a', title: 'A'}, {url: 'wix://b', title: 'B'}];
let Linking;

beforeEach(() => Linking = sinon.stub(require('react-native').Linking));

it('should render links', () => {
const drv = new LinksDriver().setProps({links});
expect(drv.getLinkTitles()).to.deep.equal(['A', 'B']);
});

it('should open URL on press', () => {
new LinksDriver(Linking).setProps({links}).tapLink('A');
expect(Linking.openURL).to.be.calledWith('wix://a')
});
});
#+END_SRC

** API

Detailed [[file:API.md][API]].