unit-jest plugin for svelte-cli

Usage no npm install needed!

<script type="module">
  import svelCliPluginUnitJest from 'https://cdn.skypack.dev/@svel/cli-plugin-unit-jest';



unit-jest plugin for svelte-cli

Injected Commands

  • svelte-cli-service test:unit

    Run unit tests with Jest. Default testMatch is <rootDir>/(tests/unit/**/*.spec.(js|jsx|ts|tsx)|**/__tests__/*.(js|jsx|ts|tsx)) which matches:

    • Any files in tests/unit that end in .spec.(js|jsx|ts|tsx);
    • Any js(x)/ts(x) files inside __tests__ directories.

    Usage: svelte-cli-service test:unit [options] <regexForTestFiles>

    All Jest command line options are also supported.

Debugging Tests

Note that directly running jest will fail because the Babel preset requires hints to make your code work in Node.js, so you must run your tests with svelte-cli-service test:unit.

If you want to debug your tests via the Node inspector, you can run the following:

# macOS or linux
node --inspect-brk ./node_modules/.bin/svelte-cli-service test:unit

# Windows
node --inspect-brk ./node_modules/@svel/cli-service/bin/svelte-cli-service.js test:unit


Jest can be configured via jest.config.js in your project root, or the jest field in package.json.

Installing in an Already Created Project

vue add @svel/unit-jest

Transform dependencies from /node_modules

By default, jest doesn't transform anything from /node_modules.

Since jest runs in node, we also don't have to transpile anything that uses modern ECMAScript features as Node >=8 already supports these features, so it's a sensible default. cli-plugin-jest also doesn't respect the transpileDependencies option in svelte.config.js for the same reason.

However, we have (at least) three cases where we do need to transpile code from /node_modules in jest:

  1. Usage of ES6 import/export statements, which have to be compiled to commonjs module.exports
  2. Single File Components (.vue files) which have to be run through vue-jest
  3. Typescript code

To do this, we need to add an exception to the tranformIgnorePatterns option of jest. This is its default value:

transformIgnorePatterns: ['/node_modules/']

We have to add exceptions to this pattern with a RegExp negative lookahead:

transformIgnorePatterns: ['/node_modules/(?!name-of-lib-o-transform)']

To exclude multiple libraries:

transformIgnorePatterns: ['/node_modules/(?!lib-to-transform|other-lib)']