javascript 使用 mocha 的内置承诺支持测试失败的承诺
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testing failed promises with mocha's built-in promise support
提问by RoyM
How should I be testing, with mocha and chai, that my promise has failed?
我应该如何用 mocha 和 chai 测试我的承诺是否失败？
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
我很困惑，因为我最初认为我应该使用 'mocha-as-promised'，但该包现在已被弃用（我使用的是 mocha 2.1.0），建议只使用现在内置的承诺测试摩卡。见：https: //github.com/domenic/mocha-as-promised
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?
另一篇文章建议取消 it() 回调中的“done”参数——我不确定我明白为什么，因为我理解传递“done”参数是一种表示测试正在被异步测试的方式。请参阅：如何使用 mocha 和 chai 正确测试 promise？
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.
无论如何，我已经尝试将我的问题简化为以下代码 - 请帮我修改它，以便我可以测试我的承诺确实失败了。
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);
});
回答by RoyM
Some more digging, and it appears the right way is to add an additional catch block, like so...
更多的挖掘，看起来正确的方法是添加一个额外的catch块，就像这样......
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);
});
I'm interested in alternative ideas, or confirmation that this is fine the way it is.. thanks.
我对其他想法很感兴趣，或者确认这是很好的方式......谢谢。
UPDATE:
更新：
Ben - I now grok what you were saying, esp. after the terse but helpful comment from Benjamin G.
本 - 我现在明白你在说什么，尤其是。在 Benjamin G 简短但有用的评论之后。
To summarize:
总结一下：
When you pass in a doneparameter, the test is expected to trigger it's 'done-ness' by calling the done()function;
当你传入一个done参数时，测试应该通过调用done()函数来触发它的“完成” ；
When you don't pass in a doneparameter, it normally only works for synchronous calls. However,
if you returna 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:
当您不传入done参数时，它通常仅适用于同步调用。但是，如果您返回承诺，则 mocha 框架（mocha > 1.18）将捕获通常会被吞噬的任何失败（根据承诺规范）。这是一个更新的版本：
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');
});
});
回答by Ben
You can return a promise to signal that the test is asynchronous:
您可以返回一个承诺以表示测试是异步的：
function something() {
return Q.reject(Error('fail'));
}
it('should reject', function() {
return something().then(function() {
throw new Error('expected rejection');
},
function() {
return 'passed :]';
});
});
回答by fearless_fool
chai-as-promisedprovides a clean testing framework for Promises:
chai-as-promised为 Promise 提供了一个干净的测试框架：
$ npm install chai-as-promised
In your test file:
在您的测试文件中：
var chai = require('chai');
var expect = chai.expect;
var chaiAsPromised = require("chai-as-promised");
chai.use(chaiAsPromised);
...
it('resolves as promised', function() {
return expect(Promise.resolve('woof')).to.eventually.equal('woof');
});
it('rejects as promised', function() {
return expect(Promise.reject('caw')).to.be.rejectedWith('caw');
});
This feels clean and intuitive. But you can accomplish something similar without chai-as-promised like this:
这感觉干净和直观。但是你可以在没有 chai-as-promised 的情况下完成类似的事情：
it('resolved as promised', function() {
return Promise.resolve("woof")
.then(function(m) { expect(m).to.equal('woof'); })
.catch(function(m) { throw new Error('was not supposed to fail'); })
;
});
it('rejects as promised', function() {
return Promise.reject("caw")
.then(function(m) { throw new Error('was not supposed to succeed'); })
.catch(function(m) { expect(m).to.equal('caw'); })
;
});
