Dainte

Painless testing for Svelte components

#svelte #testing

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Dainte

Painless testing for Svelte components, inspired by Enzyme.

🥂 Test Svelte runtime and SSR simultanously
🎭 Zero-config compatible with Jest
🤖 Low-level compile options to ensure that tests match prod
🔎 Component "state" introspection

Usage

`dainte.compile`

result: {
    // Compiled Svelte component class
    Component,

    // Alias to component as specified or inferred name
    [name],
} = await dainte.compile(source: string, options?: {...})

Creates a compiled Svelte component class from a source file path.

The following options can be passed to compile, including svelte.compile options. The dev option defaults to true for testing. None are required:

option	default	description
`name`	`'Component'`	Name of the component class, inferred from filename
`dev`	`true`	Perform runtime checks and provide debugging information
`immutable`	`false`	You promise not to mutate any objects
`hydratable`	`false`	Enables the hydrate: true runtime option
`legacy`	`false`	Generates code that will work in IE9 and IE10
`accessors`	`false`	Getters and setters will be created for the component's props
`css`	`true`	Include CSS styles in JS class
`generate`	`'dom'`	Create JS DOM class or object with `.render()`
`inspect`	`false`	Include `instance.inspect()` accessor
`plugins`	`[svelte(), resolve()]`	Advanced option to manually specify Rollup plugins for bundling.

Example

import { compile } from 'dainte'

const { App } = await compile('./App.svelte')

const app = new App({
    target: document.body,
})

`dainte.mount`

result: {
    // Svelte component instance
    instance,

    // Compiled JS component class
    Component,

    // JSDom window and document where component is mounted.
    window,
    document,

    // Alias to the Component with specified or inferred name
    [name],

    // Alias to the instance with lowercase specified or inferred name
    [lowercase(name)],
}  = await mount(source: string, options?: {...})

Creates an instance of a component from a source file path. Mounts the instance in a JSDom.

All compile options can also be passed to mount. Additionally, these options, including the component initialisation options, can be provided:

option	default	description
`html`	`'<body></body>'`	HTML to initiate the JSDom instance with
`target`	`'body'`	Render target (as a query selector, not a DOM element as in Svelte initialisation)
`anchor`	`null`	Render anchor (as a query selector, not a DOM element as in Svelte initialisation)
`props`	`{}`	An object of properties to supply to the component
`hydrate`	`false`	Upgrade existing DOM instead of replacing it
`intro`	`false`	Play transitions on initial render

A svelte.tick is awaited between mounting the instance and resolving the mount promise so that the DOM is full initialized. An additional svelte.tick should be awaited between updating the component and reading from the DOM.

Example

import { mount } from 'dainte'
import { tick } from 'svelte'

const { app, document } = await mount('./App.svelte')
app.$set({ answer: 42 })
await tick()

expect(document.querySelector('#answer').textContent).toBe('42')

`dainte.render`

result: {
    head,
    html,
    css,
} = await dainte.render(source: string, options?: {...})

Wraps Svelte's server-side Component.render API for rendering a component to HTML.

The following options can be passed to render, including svelte.compile options. The dev option defaults to true for testing. None are required:

option	default	description
`dev`	`true`	Perform runtime checks and provide debugging information
`immutable`	`false`	You promise not to mutate any objects
`hydratable`	`false`	Enables the hydrate: true runtime option
`css`	`true`	Include CSS styles in JS class
`preserveComments`	`false`	HTML comments will be preserved
`preserveWhitespace`	`false`	Keep whitespace inside and between elements as you typed it
`plugins`	`[svelte(), resolve()]`	Advanced option to manually specify Rollup plugins for bundling.

Example

import { render } from 'dainte'

const { html } = await render('./App.svelte')
// '<div id="answer">42</div>'

`instance.inspect`

variables: {
    // Snapshot of all top-level variables and imports
} = instance.inspect()

Compiling with inspect: true adds a inspect() function to the component instance. Calling the function returns a snapshot object of all top-level variables and their current values. Snapshot values are not reactive and inspect() must be called again to retrieve updated values.

Example

import { mount } from 'dainte'

const { app } = await mount('./App.svelte', { inspect: true })
const { answer } = app.inspect()
// 42

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