如何在nodejs上使用mocha对控制台输出进行单元测试？

How to unit test console output with mocha on nodejs?

提问by Kemel Zaidan

Take into account the following example Javascript code below:

考虑以下示例 Javascript 代码：

function privateFunction (time) {
  if (time < 12) { console.log('Good morning'); }
  if (time >= 12 && time <19) { console.log('Good afternoon'); }
  else { console.log('Good night!'); }
};

How should I unit test that on nodejs using mocha (and possibly sinonjs), noticing that this is a private function called inside a module? I need to pass in the argument and check if the function is logging the right thing to the console.

我应该如何使用 mocha（可能还有 sinonjs）对 nodejs 进行单元测试，注意到这是一个在模块内部调用的私有函数？我需要传入参数并检查该函数是否将正确的内容记录到控制台。

Can I do the same with console.warnand console.error?

我可以用console.warnand做同样的事情console.error吗？

回答by robertklep

I prefer mocha-sinonover "plain" sinon because it integrates nicely with Mocha.

我更喜欢mocha-sinon“普通”的 sinon，因为它与 Mocha 很好地集成在一起。

Example:

例子：

var expect = require('chai').expect;
require('mocha-sinon');

// Function to test, can also be in another file and as long as it's
// being called through some public interface it should be testable.
// If it's not in any way exposed/exported, testing will be problematic.
function privateFunction (time) {
  if (time < 12) { console.log('Good morning'); }
  if (time >= 12 && time <19) { console.log('Good afternoon'); }
  else { console.log('Good night!'); }
}

describe('privateFunction()', function() {

  beforeEach(function() {
    this.sinon.stub(console, 'log');
  });

  it('should log "Good morning" for hours < 12', function() {
    privateFunction(5);
    expect( console.log.calledOnce ).to.be.true;
    expect( console.log.calledWith('Good morning') ).to.be.true;
  });

  it('should log "Good afternoon" for hours >= 12 and < 19', function() {
    privateFunction(15);
    expect( console.log.calledOnce ).to.be.true;
    expect( console.log.calledWith('Good afternoon') ).to.be.true;
  });

  it('should log "Good night!" for hours >= 19', function() {
    privateFunction(20);
    expect( console.log.calledOnce ).to.be.true;
    expect( console.log.calledWith('Good night!') ).to.be.true;
  });

});

One potential issue: some Mocha reporters use console.logas well, so the tests that stub it may not yield any output.

一个潜在问题：一些 Mocha 记者也使用console.log，因此存根它的测试可能不会产生任何输出。

There's a workaround, but it's not ideal either because it will intersperse Mocha output with the output from privateFunction(). If that's not a problem, replace beforeEach()with this:

有一个解决方法，但它也不理想，因为它会将 Mocha 输出与privateFunction(). 如果这不是问题，请替换beforeEach()为：

beforeEach(function() {
  var log = console.log;
  this.sinon.stub(console, 'log', function() {
    return log.apply(log, arguments);
  });
});

回答by Eliran Malka

ignoring the fact that it's a private function, i would take a couple of steps; refactor my code for better separation of concerns, and utilise this separation with test doubles.

忽略它是一个私有函数的事实，我会采取几个步骤；重构我的代码以更好地分离关注点，并将这种分离用于测试替身。

• take all the side effects outside to their own modules (the side effect here is writing to the console):

  out.js

  function log (message) {
    console.log(message);
  };
  
  module.exports = {log};
  

  app.js

  const {log} = require('out');
  
  function greeter (time) {
    if (time < 12) {
      log('Good morning');
    }
    if (time >= 12 && time < 19) {
      log('Good afternoon');
    } else {
      log('Good night!');
    }
  };
  
  module.exports = {greeter};
  

• use some module proxy/spy, like proxyquireto replace the whole out writer when testing:

  app.spec.js

  describe('output writers', function(){
  
    const fakeOut = {
      log: sinon.spy(),
    };
  
    const app = proxyquire('./app', {
      'out': fakeOut
    });
  
    it('should log to the fake out', function(){
      app.greeter(15);
      assert(fakeOut.log.calledOnce);
    });
  });
  

• 把所有的副作用都放到他们自己的模块中（这里的副作用是写到控制台）：

  输出.js

  function log (message) {
    console.log(message);
  };
  
  module.exports = {log};
  

  应用程序.js

  const {log} = require('out');
  
  function greeter (time) {
    if (time < 12) {
      log('Good morning');
    }
    if (time >= 12 && time < 19) {
      log('Good afternoon');
    } else {
      log('Good night!');
    }
  };
  
  module.exports = {greeter};
  

• 在测试时使用一些模块代理/间谍，例如proxyquire来替换整个输出编写器：

  应用规范.js

  describe('output writers', function(){
  
    const fakeOut = {
      log: sinon.spy(),
    };
  
    const app = proxyquire('./app', {
      'out': fakeOut
    });
  
    it('should log to the fake out', function(){
      app.greeter(15);
      assert(fakeOut.log.calledOnce);
    });
  });
  

回答by Angelos Pikoulas

If your purpose is solelyto test console output, I would suggest instead of stubs / spies etc on method calls, to use something like:

如果您的目的仅仅是测试控制台输出，我建议您不要在方法调用上使用存根/间谍等，而是使用以下内容：

• test-console

• monitor stdout/stderr instead, you can use ideas from this gist

• 测试控制台

• 改为监视 stdout/stderr，您可以使用此要点中的想法