text: // @flow
  import type { Compiler, Stats } from '../types';
  
  export default function registerReadyCallback(compiler: Compiler, cb: (err: ?(Error | string), stats: ?Stats) => void) {
    compiler.hooks.failed.tap('mocha-webpack', cb);
    compiler.hooks.done.tap('mocha-webpack', (stats: Stats) => {
      if (stats.hasErrors()) {
        const jsonStats = stats.toJson();
        const [err] = jsonStats.errors;
        cb(err, stats);
      } else {
        cb(null, stats);
      }
    });
  }
  