Svelte Jester

Overview

This product analysis will focus on a library called svelte-jester. The library is used for testing Svelte applications with Jest. The analysis will cover key features, installation instructions, and a summary of the content.

Features

• Svelte Testing: svelte-jester allows for easy testing of Svelte applications with Jest.
• Preprocess Options: The library supports various preprocess options, including support for TypeScript and Babel.
• ESM and CJS versions: svelte-jester provides both ESM (ECMAScript module) and CJS (CommonJS) versions for different project setups.

ESM version

To use the ESM version of svelte-jester, add the following to your Jest config:

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

CJS (CommonJS) version

For the CJS version, add the following to your Jest config:

"transform": {
  "^.+\\.svelte$": "svelte-jester/dist/transformer.cjs"
},
"moduleFileExtensions": [
  "js",
  "ts",
  "svelte"
]

Babel (only for CJS)

If you need to use Babel for the CJS version, install the required packages:

npm install @babel/core @babel/preset-env babel-jest -D

Add the following to your Jest config:

"transform": {
  "^.+\\.svelte$": "svelte-jester/dist/transformer.cjs"
},
"moduleFileExtensions": [
  "js",
  "ts",
  "svelte"
],
"transformIgnorePatterns": [
  "node_modules/(?!(svelte)|(my-lib))"
],
"transformOptions": {
  "babelConfig": true
}

TypeScript

To enable TypeScript support, install the necessary packages:

npm install typescript svelte-preprocess ts-jest -D

ESM version

Create a svelte.config.js file at the root of your project with the following configuration:

const sveltePreprocess = require('svelte-preprocess');

module.exports = {
  preprocess: sveltePreprocess()
};

In your Jest config, enable preprocessing for svelte-jester and add ts-jest as a transform:

"transform": {
  "^.+\\.svelte$": [
    "svelte-jester",
    {
      "preprocess": true
    }
  ],
  ".+\\.(css|styl|less|sass|scss)$": "jest-transform-css"
},
"moduleFileExtensions": [
  "js",
  "ts",
  "svelte"
]

CJS version

Create a svelte.config.js file at the root of your project with the following configuration:

const sveltePreprocess = require('svelte-preprocess');

module.exports = {
  preprocess: sveltePreprocess()
};

In your Jest config, enable preprocessing for svelte-jester and add ts-jest as a transform:

"transform": {
  "^.+\\.svelte$": [
    "svelte-jester/dist/transformer.cjs",
    {
      "preprocess": true
    }
  ],
  ".+\\.(css|styl|less|sass|scss)$": "jest-transform-css"
},
"moduleFileExtensions": [
  "js",
  "ts",
  "svelte"
]

Note: TypeScript supports ES modules, so if you were previously using babel-jest for ES module transpilation, you can remove babel-jest, babel, and any associated presets and config. However, if you still want to use ES modules in .js files, you need to configure ts-jest accordingly.

Summary

svelte-jester is a library that facilitates testing of Svelte applications using Jest. It provides support for different preprocess options, including TypeScript and Babel. The library offers ESM and CJS versions to accommodate different project setups. The installation process requires configuring the Jest config file appropriately based on the chosen version and preprocess options.