Stencil
Stencil is a library for building reusable, scalable component libraries. You can test Stencil components directly in a real browser using WebdriverIO and its browser runner.
Setup
To set up WebdriverIO within your Stencil project, follow the instructions in our component testing docs. Make sure to select stencil as preset within your runner options, e.g.:
// wdio.conf.js
export const config = {
// ...
runner: ['browser', {
preset: 'stencil'
}],
// ...
}
In case you use Stencil with a framework like React or Vue, you should keep the preset for these frameworks.
You can then start the tests by running:
npx wdio run ./wdio.conf.ts
Writing Tests
Given you have the following Stencil components:
import { Component, Prop, h } from '@stencil/core'
@Component({
tag: 'my-name',
shadow: true
})
export class MyName {
@Prop() name: string
normalize(name: string): string {
if (name) {
return name.slice(0, 1).toUpperCase() + name.slice(1).toLowerCase()
}
return ''
}
render() {
return (
<div class="text">
<p>Hello! My name is {this.normalize(this.name)}.</p>
</div>
)
}
}
render
In your test use the render method from @wdio/browser-runner/stencil to attach the component to the test page. To interact with the component we recommend using WebdriverIO commands as they behave closer to actual user interactions, e.g.:
import { expect } from '@wdio/globals'
import { render } from '@wdio/browser-runner/stencil'
import MyNameComponent from './components/Component.tsx'
describe('Stencil Component Testing', () => {
it('should render component correctly', async () => {
await render({
components: [MyNameComponent],
template: () => (
<my-name name={'stencil'}></my-name>
)
})
await expect($('.text')).toHaveText('Hello! My name is Stencil.')
})
})
Render Options
The render method provides the following options:
components
An array of components to test. Component classes can be imported into the spec file, then their reference should be added to the component array to be used throughout the test.
Type: CustomElementConstructor[]
Default: []
flushQueue
If false, do not flush the render queue on the initial test setup.
Type: boolean
Default: true
template
The initial JSX that is used to generate the test. Use template when you want to initialize a component using their properties, instead of their HTML attributes. It will render the specified template (JSX) into document.body.
Type: JSX.Template
html
The initial HTML used to generate the test. This can be useful to construct a collection of components working together, and assign HTML attributes.
Type: string
language
Sets the mocked lang attribute on <html>.
Type: string
autoApplyChanges
By default, any changes to component properties and attributes must env.waitForChanges() to test the updates. As an option, autoApplyChanges continuously flushes the queue in the background.
Type: boolean
Default: false
attachStyles
By default, styles are not attached to the DOM and they are not reflected in the serialized HTML. Setting this option to true will include the component's styles in the serializable output.
Type: boolean
Default: false
Render Environment
The render method returns an environment object that provides certain utility helpers to manage the component's environment.
flushAll
After changes have been made to a component, such as an update to a property or attribute, the test page does not automatically apply the changes. To wait for, and apply the update, call await flushAll()
Type: () => void
unmount
Removes the container element from the DOM.
Type: () => void
styles
All styles defined by components.
Type: Record<string, string>
container
Container element in which the template is being rendered.
Type: HTMLElement
$container
The container element as a WebdriverIO element.
Type: WebdriverIO.Element
root
The root component of the template.
Type: HTMLElement
$root
The root component as a WebdriverIO element.
Type: WebdriverIO.Element
waitForChanges
Helper method to wait for the component to be ready.
import { render, waitForChanges } from '@wdio/browser-runner/stencil'
import { MyComponent } from './component.tsx'
const page = render({
components: [MyComponent],
html: '<my-component></my-component>'
})
expect(page.root.querySelector('div')).not.toBeDefined()
await waitForChanges()
expect(page.root.querySelector('div')).toBeDefined()
Element Updates
If you define properties or states in your Stencil component you have to manage when these changes should be applied to the component to be re-rendered.
Examples
You can find a full example of a WebdriverIO component test suite for Stencil in our example repository.
