求助一道笔试题，有关js并发执行异步任务

/**

• --- 问题描述 ---
• 给出一组异步任务方法，和允许同时执行的个数，实现一个方法，用于并发执行异步任务
• --- 说明 ---
• • 当有任务执行完毕后，自动补充任务，始终保持正在执行的任务有 concurrency 个
• • 返回 { resolved: [], rejected: [] }

*/

const assert = require('assert');

async function parallel(tasks, concurrency) {
    //此处填写代码
}

/测试部分/

module.exports = async function doTest() {
  try {
    const child_process = require('child_process');
    const fs = require('fs');
    const path = require('path');
    const util = require('util');
    const readFile = util.promisify(fs.readFile);
    const exec = util.promisify(child_process.exec);

    const tasks = [
      () => readFile(__filename, 'utf-8'),
      () => Promise.resolve('foo'),
      () => exec('npm -v'),
      () => readFile(path.join(__dirname, '../package.json'), 'utf-8'),
      () => process.cpuUsage(),
      () => exec('node -v'),
      () => Promise.reject(new Error('bar')),
      () => exec('ls -al'),
      () => new Promise(resolve => process.nextTick(resolve)),
      () => exec('whoami')
    ];
    const { resolved, rejected } = await parallel(tasks, 3);
    assert.equal(resolved.length, 9);
    assert.equal(rejected.length, 1);
    return '通过';
  } catch (err) {
    return '不通过';
  }
};