Testing Svelte with Jest

compile.js

const rollup = require('rollup');
const esm = require('esm');

const { config } = esm(module)('../rollup.config');

function generateOptions(filePath, name) {
  return {
    input: { input: filePath, plugins: config.plugins },
    output: {
      file: `./dist/test/${name}.js`,
      format: 'cjs',
    },
  };
}

function compile(filePath, name) {
  const { input, output } = generateOptions(filePath, name);

  return rollup.rollup(input)
    .then(bundle => bundle.generate(output));
}

module.exports = { compile };

package.json

{
  "jest": {
    "testMatch": [
      "**/test/**/*.js"
    ],
    "transform": {
      "\\.js$": "babel-jest",
      "\\.(html|svelte)$": "./test/transform"
    },
    "transformIgnorePatterns": [
      "/node_modules/(?!svelte).+\\.js$"
    ],
    "moduleFileExtensions": [
      "js",
      "json",
      "html",
      "svelte"
    ]
  }
}

transform.js

const deasync = require('deasync');
const { compile } = require('./compile');

module.exports.process = (_s, filePath, _c, _o) => {
  let code, map;
  compile(filePath, 'App', {}).then(comp => {
    code = comp.code;
    map = comp.map;
  });

  deasync.loopWhile(() => !code && !map);

  return { code, map };
};