Mocha，should-当测试包含promise的异步函数时，断言错误是沉默的

Question

我有个小问题困扰着我。。下面的代码显示了一个异步测试，在那个测试中我们测试了一个我们无法控制的代码（测试用黑盒，我可以更改它）。

blackbox代码在事件完成后分派事件，测试侦听此事件并断言数据。

问题是，当有断言错误时，异常是由promise错误处理程序而不是由测试框架抛出和产生的，因此done函数永远不会执行，我们得到了这个测试的超时错误。

它很容易解决它的尝试和安培；catch在it()块内，但是总是使用try&是一个好的实践吗；在it()块内捕获？到目前为止，我信任测试框架来处理异常

null

这里的提示帮助我解决了这个问题，但我不喜欢这些解决方案:https://github.com/mochajs/mocha/issues/1128.issuecomment-40866763

它与其他类似的问题不同，因为在it()块中，我们没有任何对promise对象的引用。

describe.only("test", function () {

  var event;

  // blackbox simulates a code we have no controler over
  // inside this code we have a promise, when this promise resolves it triggers event
  var blackbox = function () {
    var promise = new Promise(function (resolve, reject) {
      resolve();
    });

    promise.then(function () {
      event(4);
    }).catch(function (e) {
      console.log(e);
    });
  };

  it("async with blackbox promise", function (done) {
    // this simulates event listenner, when the event is triggered the code executes
    event = function (data) {
      // this assertion works and everything is fine
      data.should.be.equal(4);
      // this assertion thrown exception that is being cought by the promise reject handler and
      // isnt cought by the testing framework (chai / mocha)
      data.should.be.equal(5);
      // because the exception is thrown we never reach the done
      done();
    };

    blackbox();

  });
});

Answer 1

在 中测试承诺的方式是返回承诺，并让它来决定何时失败或不失败。

因此，第一步是在 函数中使承诺可用:

// blackbox simulates a code we have no controler over
// inside this code we have a promise, when this promise resolves it triggers event
var blackbox = function () {
  var promise = new Promise(function (resolve, reject) {
    resolve();
  });

  return promise.then(function () {
    event(4);
  });
  // do not catch here unless you want the test to not fail on error
};

现在让我们更改测试代码以处理承诺:

it("async with blackbox promise", function () {
  // this simulates event listenner, when the event is triggered the code executes
  event = function (data) {
    // this assertion works and everything is fine
    data.should.be.equal(4);
    // this assertion thrown exception that is being cought by the promise reject handler
    data.should.be.equal(5);
  };
  // mocha will append a rejection handler to this promise here and fail if it gets called
  return blackbox();

});