Skip to main content

Setup

We recommend using Vitest but you're free to use the library with any testing framework and runner you're comfortable with.

Vitest​

  1. Install Vitest and jsdom

    npm install --save-dev vitest jsdom

  2. Add the following to your package.json

    {
      "scripts": {
        "test": "vitest run src",
        "test:watch": "vitest src"
      }
    }

  3. You'll need to compile the Svelte components before using them in Vitest, so you need to install @sveltejs/vite-plugin-svelte and Vite

    npm install --save-dev @sveltejs/vite-plugin-svelte vite

  4. Add a vitest.config.ts configuration file to the root of your project

    import {defineConfig} from 'vite'
    import {svelte} from '@sveltejs/vite-plugin-svelte'

    export default defineConfig({
      plugins: [svelte({hot: !process.env.VITEST})],
      test: {
        include: ['src/**/*.{test,spec}.{js,mjs,cjs,ts,mts,cts,jsx,tsx}'],
        globals: true,
        environment: 'jsdom',
      },
    })

  5. This is optional but it is recommended, you can install jest-dom to add handy assertions to Jest

    5.1 Install jest-dom

    npm install --save-dev @testing-library/jest-dom

    5.2 import @testing-library/jest-dom at the start of your test files

    import '@testing-library/jest-dom'

  6. Create your component and a test file (checkout the rest of the docs to see how) and run the following command to run the tests.

    npm run test

SvelteKit​

To use Vitest with SvelteKit install vitest-svelte-kit, which includes a preconfigured Vitest configuration for SvelteKit projects. You can take a look at the vitest-svelte-kit configuration docs for further instructions.

Jest​

  1. Install Jest & jest-environment-jsdom

    npm install --save-dev jest jest-environment-jsdom

  2. Add the following to your package.json

    {
      "scripts": {
        "test": "jest src",
        "test:watch": "npm run test -- --watch"
      }
    }

  3. You'll need to compile the Svelte components before using them in Jest, so we need to install svelte-jester

    npm install --save-dev svelte-jester

  4. Add the following Jest configuration to your package.json

    {
      "jest": {
        "transform": {
          "^.+\\.svelte$": "svelte-jester"
        },
        "moduleFileExtensions": ["js", "svelte"],
        "testEnvironment": "jsdom"
      }
    }

  5. If you are using ES6 modules in your project you have to add Jest's babel transform setting (it is set by default, but since we are overriding the transform config, we have to add it explicitly)

    5.1 Install babel-jest

    npm install --save-dev babel-jest

    5.2. Add a basic .babelrc configuration

    {
      "presets": [["@babel/preset-env", {"targets": {"node": "current"}}]]
    }

    5.3. Update the Jest transform configuration

    "transform": {
      "^.+\\.js$": "babel-jest",
      "^.+\\.svelte$": "svelte-jester"
    },

  6. This is optional but it is recommended, you can install jest-dom to add handy assertions to Jest

    6.1 Install jest-dom

    npm install --save-dev @testing-library/jest-dom

    6.2 Add the following to your Jest configuration in package.json

    {
      "setupFilesAfterEnv": ["@testing-library/jest-dom/extend-expect"]
    }

  7. Create your component + test file (checkout the rest of the docs to see how) and run it

    npm run test

Typescript​

To use Typescript with Jest, you'll need to install and configure svelte-preprocess and ts-jest. For full instructions, see the svelte-jester docs.

Preprocessors​

If you'd like to also include any Svelte preprocessors then simply follow the instructions over at svelte-jester.