Test Renderer

@threlte/test

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

npm i @threlte/test

It supports Svelte 5 + Threlte 8 onwards.

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, // ({ count?: number; 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 })

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>
  let { onclick } = $props()
</script>

<T.Mesh {onclick} />

We can write a test like this:

const onclick = vi.fn()
const { render, fireEvent } = render(Scene, {
  props: { 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

@threlte/test currently only supports 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, like happy-dom or vitest browser mode.

Limitations

The test renderer runs in a node.js environment, unless if running in vite browser mode. It creates a Threlte context and renders your component with this context provided. This must be considered when testing <Canvas> or WebGLRenderer related configuration and behavior.