@threlte/test

@threlte/test is a lightweight component testing toolkit for Threlte.

npm i @threlte/test

It supports Svelte 4 + Threlte 7 and Svelte 5 + Threlte 8.

import { describe, it, expect } from 'vitest'
import { render } from '@threlte/test'
import Scene from './Scene.svelte'

describe('Scene', () => {
  it('creates a box mesh with a boxGeometry and meshStandardMaterial', () => {
    const { scene } = render(Scene)

    const mesh = scene.getObjectByProperty('isMesh', true) as Mesh
    expect(mesh).toBeDefined()
    expect(mesh.material).toBeInstanceOf(MeshStandardMaterial)
    expect(mesh.geometry).toBeInstanceOf(BoxGeometry)
  })
})

It provides a function, render, which will instantiate a Threlte context and whatever component you pass to it.

Calling render will provide useful tools for testing your component's behavior.

const {
  component, // SvelteComponent
  scene, // THREE.Scene
  camera, // CurrentWritable<THREE.Camera>
  advance, // (delta?: number) => void
  fireEvent, // (object3D: THREE.Object3D, event, payload) => Promise<void>
  rerender, // (props) => Promise<void>
  unmount, // () => void
} = render(Component)

Scene

scene is the THREE.Scene created by a Threlte context without any modifications. Querying objects from it can be useful for verifying that your component is doing what you expect it to.

Advance

In the test renderer environment, Threlte's render mode is set to manual. If you wish to test results produced by running useTask, you must call advance. advance is very similar to the function of the same name returned by the useThrelte hook, but it advances at a fixed rate (16ms) regardless of environment. The number of times called and delta can also be configured when calling it.

// Runs advance() 10 times with a 33.3ms delta
advance({ delta: 33.3, count: 10 })

advance will also return a flag indicating whether calling it resulted in a frame invalidation.

const { frameInvalidated } = advance()

fireEvent

If your component uses the interactivity plugin, you can test events using the fireEvent function. Let's say we have a component like this:

<script lang="ts">
  export let onClick
</script>

<T.Mesh on:click={onClick}>...</T.Mesh>

We can write a test like this:

const onClick = vi.fn()
const { render, fireEvent } = render(Scene, { onClick })

const mesh = scene.getObjectByName('myMesh')
await fireEvent(mesh, 'click', someOptionalCustomPayload)
expect(onClick).toHaveBeenCalledOnce()

Note that if you use the event object, you will have to design a mock payload.

Setup

We recommend using @threlte/test with Vitest as your test runner. To get started, add the threlteTesting plugin to your Vite or Vitest config.

// vite.config.js
import { svelte } from '@sveltejs/vite-plugin-svelte'
import { threlteTesting } from '@threlte/test/vite'

export default defineConfig({
  plugins: [
    svelte(),
    threlteTesting(),
  ]
});

Additionally, the Vitest environment must be set to a DOM enviroment.

Limitations

The test renderer runs in a node.js environment, and it does not attempt to mock a webgl canvas, which can become quite complicated. Instead, it creates a Threlte context and renders your component as a child of a Threlte <SceneGraphObject>. This means that testing <Canvas> or WebGLRenderer related configuration and behavior won't work.

This libary's primary purpose, however, is to allow you to test whether your component works in isolation as you intend it to work.