使用Mocha内置的Promise支持测试失败的Promise [英] testing failed promises with mocha's built-in promise support

问题描述

我应该如何与mocha和chai一起测试我的诺言失败了?

How should I be testing, with mocha and chai, that my promise has failed?

我很困惑，因为我最初以为我应该使用'mocha-as-promised'，但是那 现在已弃用该软件包(我使用的是Mocha 2.1.0)，并建议 只需使用摩卡咖啡内置的承诺测试即可. 参见: https://github.com/domenic/mocha-as-promised

I am confused, because I initially thought I should be using 'mocha-as-promised', but that package is now deprecated (I'm using mocha 2.1.0), with the advice to just use the promise testing that's now built into mocha. see: https://github.com/domenic/mocha-as-promised

另一篇文章建议取消对 it()回调-不知道我为什么会这样，因为我知道 传递"done"参数是表明测试已通过的方式 正在异步测试. 请参阅:如何正确地使用摩卡和柴对诺言进行测试?

Another post recommends doing away with the 'done' argument to the it() callback - not sure I understand why, since my understanding that passing in the 'done' parameter was the way to signal that a test was being tested asynchronously. see: How do I properly test promises with mocha and chai?

无论如何，我试图将问题简化为以下代码-请帮助我进行修改，以便我可以测试我的诺言确实失败了.

Anyway, I've tried to reduce my issue to the below code - please help me modify this so that I can test that my promise indeed fails.

it.only("do something (negative test)", function (done) {

  var Q = require('q');

  function makePromise() {
    var deferred = Q.defer();
    deferred.reject(Error('fail'));
    return deferred.promise;
  };

  makePromise()
  .then(done, done);

});

推荐答案

进行更多的挖掘，看来正确的方法是添加一个额外的catch块，就像这样...

Some more digging, and it appears the right way is to add an additional catch block, like so...

it.only("do something (negative test)", function (done) {

  var Q = require('q');

  function makePromise() {
    var deferred = Q.defer();
    deferred.reject(Error('fail'));
    return deferred.promise;
  };

  makePromise()
  .catch(function(e) {
    expect(e.message).to.equal('fail');
  })
  .then(done, done);

});

我对其他想法感兴趣，或者确认这是一种很好的方式..谢谢.

I'm interested in alternative ideas, or confirmation that this is fine the way it is.. thanks.

更新:

Ben-现在，我想知道你在说什么，尤其是.在本杰明·G的简短但有益的评论之后.

总结:

当您传递一个done参数时，预期该测试将通过调用done()函数来触发其完成"；

When you pass in a done parameter, the test is expected to trigger it's 'done-ness' by calling the done() function;

当您不传递done参数时，它通常仅适用于同步调用.然而， 如果您 返回 一个承诺，那么mocha框架(mocha> 1.18)将捕获通常会被吞噬的所有失败(根据promise规范).这是更新的版本:

When you don't pass in a done parameter, it normally only works for synchronous calls. However, if you return a promise, the mocha framework (mocha >1.18) will catch any failures that normally would have been swallowed (per the promises spec). Here is an updated version:

it.only("standalone neg test for mocha+promises", function () {

  var Q = require('q');

  function makePromise() {
    var deferred = Q.defer();
    deferred.reject(Error('fail'));
    return deferred.promise;
  };

  return makePromise()
  .catch(function(e) {
    expect(e.message).to.equal('fail');
  });

});

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