make jest behave using (webpack) loader-runner

jest-webpack-loader.js

const deasync = require('deasync')
const runLoaders = deasync(require('loader-runner').runLoaders)
const { module: { rules } } = config = require('./webpack.base')
const fs = require('fs')

const resolveLoader = req => {
  let loader = req
  req = ~req.indexOf`?`
  if (req) {
    const index = ~req
    req = loader.substring(index)
    loader = loader.substring(0, index)
  }
  return require.resolve(loader) + (req || '')
}

exports.process = (src, resource) => {
  try {
    if (/node_modules/.test(resource)) return src
    let use, loaders = (rules || config.module.loaders)
      .find(({ test }) => resource.match(test))

    if (loaders) ({ use, loaders = use } = loaders); else return src
    loaders = typeof loaders == 'string'
      ? [ resolveLoader(loaders) ]
      : loaders.map(({ options, loader }, key) => loader
        ? { loader: require.resolve(loader), options }
        : resolveLoader(loaders[key])
      )
    const { result } = runLoaders({ resource, loaders, readResource: fs.readFile.bind(fs) })
    return result[0]
  }
  catch (e) { console.error(e) }
}