Use Jest with CoffeeScript

package.json

{
  "jest": {
    "moduleFileExtensions": [
      "js",
      "json",
      "jsx",
      "node",
      "coffee"
    ],
    "preprocessorIgnorePatterns": [ ],
    "scriptPreprocessor": "<rootDir>/test/preprocessor.js"
  }
 }

preprocessor.js

const coffee = require('coffee-script');
const babelJest = require('babel-jest');

module.exports = {
  process: (src, path) => {
    // CoffeeScript files can be .coffee, .litcoffee, or .coffee.md
    if (coffee.helpers.isCoffee(path)) {
      return coffee.compile(src, { bare: true });
    }
    if (!/node_modules/.test(path)) {
      return babelJest.process(src, path);
    }
    return src;
  }
};

In order to have the line numbers to be correct use this code:

const coffee = require('coffeescript');
const babelJest = require('babel-jest');

module.exports = {
  process: (src, filename, options) => {
    if (coffee.helpers.isCoffee(filename)) {
      let js = coffee.compile(src, {
        bare: true,
        filename: filename,
        inlineMap: true,
      });
      return babelJest.default.process(js, filename, options);
    }
    return src;
  }
};