当在Mocha测试中收听stdout时,'此套接字关闭'

Question

这个测试

it.only('should not throw', () => {
    var output = '';

    function callback(data) {
        output += data.toString();
    }

    process.stdout.on('data', callback); // error is thrown at this line
    // ...
    process.stdout.removeListener('data', callback);
})

抛出错误:

Error: This socket is closed                                                                           
    at WriteStream.Socket._writeGeneric (net.js:679:19)                                                
    at WriteStream.Socket._write (net.js:730:8)                                                        
    at doWrite (_stream_writable.js:331:12)                                                            
    at writeOrBuffer (_stream_writable.js:317:5)                                                       
    at WriteStream.Writable.write (_stream_writable.js:243:11)                                         
    at WriteStream.Socket.write (net.js:657:40)                                                        
    at Console.log (console.js:43:16)                                                                  
    at Runner.<anonymous> (node_modules\mocha\lib\reporters\spec.js:80:13)
    at emitTwo (events.js:111:20)                                                                      
    at Runner.emit (events.js:191:7)                                                                   
    at Runner.fail (node_modules\mocha\lib\runner.js:251:8)               
    at Runner.uncaught (node_modules\mocha\lib\runner.js:757:8)           
    at process.uncaught (node_modules\mocha\lib\runner.js:839:10)         
    at emitOne (events.js:96:13)                                                                       
    at process.emit (events.js:188:7)                                                                  
    at process._fatalException (bootstrap_node.js:297:26)                                              

node_modules\mocha\lib\reporters\spec.js:80:13这些摩卡线在哪里:

  runner.on('fail', function(test) {
    console.log(indent() + color('fail', '  %d) %s'), ++n, test.title);
  });

它应该测试输出代码process.stdout用spawn的,但我没能拿到这部分; 在process.stdout.on('data', ...)通话时立即抛出错误.

最新的Mocha(5.2.0)和默认配置问题仍然存在,使用中的报告器不会影响结果.

发生了什么以及如何process.stdout倾听？如果这是不可能的,那么如何在Mocha中测试产生过程的stdout呢？

Answer 1

我无法重现该错误：process.stdout.on('data', callback); // error is thrown at this line。很难说为什么它会影响你。反正process.stdout是可写流，所以data不支持事件。另一方面childProcess.stdout是从父级角度来看的可读流。

拦截子进程的 stdout 最简单的方法是：

const ch = spawn(...)
ch.stdout.on('data', d => ...) // 'd' is a buffer

如果您想针对任意生成进程的标准输出进行测试，恐怕您需要在生成进程时将自定义可写流作为子进程的标准输出传递。流需要基于文件描述符，Duplex不幸的是，如此简单的操作是行不通的。

这是一个可能的设置：

流程.js

const { spawn } = require('child_process')

module.exports = (outStream) => {
  console.log('PARENT')
  const s = spawn('node', [`${__dirname}/child.js`], { stdio: ['ignore', outStream] })

  return () => {
    console.log('PARENT-DISPOSE')
    s.kill()
  }
}

孩子.js

process.stdout.write('FROM CHILD')
setTimeout(() => process.stdout.write('FROM CHILD END'), 100)

流程规范.js

const { spawn } = require('child_process')
const fs = require('fs')

const process = require('./process.js')

// path to temporary file
const commF = `${__dirname}/comm`

it('test spawn', (done) => {
  const w = fs.createWriteStream(commF)
  let dispose

  w.on('open', () => {
    dispose = process(w)
  })

  // unfortunately I was not able to make fs.createReadStram to read data in real-time
  // so here we use another subprocess just for that
  let readProcess = spawn('tail', ['-f', commF])

  readProcess.stdout.on('data', x => {
    const d = x && x.toString()
    console.log('TEST', d) // only logs from child are present here
    if (d.startsWith('FROM CHILD END')) {
      w.close()
      fs.unlinkSync(commF)
      dispose()
      readProcess.kill()
      done()
    }
  })
}).timeout(500)

并不是说这是最好的方法：可以将其抽象化以实现可重用，并且tail可以删除依赖关系。