Mocha/Chai expect.to.throw 没有捕捉到抛出的错误 [英] Mocha / Chai expect.to.throw not catching thrown errors

问题描述

我在让 Chai 的 expect.to.throw 测试我的 node.js 应用程序时遇到问题.测试在抛出的错误上一直失败，但是如果我将测试用例包装在 try 和 catch 中，并对捕获的错误进行断言，它就可以工作.

I'm having issues getting Chai's expect.to.throw to work in a test for my node.js app. The test keeps failing on the thrown error, but If I wrap the test case in try and catch and assert on the caught error, it works.

expect.to.throw 是不是像我认为的那样不工作?

Does expect.to.throw not work like I think it should or something?

it('should throw an error if you try to get an undefined property', function (done) {
  var params = { a: 'test', b: 'test', c: 'test' };
  var model = new TestModel(MOCK_REQUEST, params);

  // neither of these work
  expect(model.get('z')).to.throw('Property does not exist in model schema.');
  expect(model.get('z')).to.throw(new Error('Property does not exist in model schema.'));

  // this works
  try { 
    model.get('z'); 
  }
  catch(err) {
    expect(err).to.eql(new Error('Property does not exist in model schema.'));
  }

  done();
});

失败:

19 passing (25ms)
  1 failing

  1) Model Base should throw an error if you try to get an undefined property:
     Error: Property does not exist in model schema.

推荐答案

你必须传递一个函数给 expect.像这样:

You have to pass a function to expect. Like this:

expect(model.get.bind(model, 'z')).to.throw('Property does not exist in model schema.');
expect(model.get.bind(model, 'z')).to.throw(new Error('Property does not exist in model schema.'));

按照你的方式，你将调用 model.get('z') 的 result 传递给 expect.但是要测试是否抛出了某些东西，您必须将一个函数传递给 expect，expect 将调用自身.上面使用的 bind 方法创建了一个新函数，当调用该函数时将调用 model.get 并将 this 设置为 model<的值/code> 并且第一个参数设置为 'z'.

The way you are doing it, you are passing to expect the result of calling model.get('z'). But to test whether something is thrown, you have to pass a function to expect, which expect will call itself. The bind method used above creates a new function which when called will call model.get with this set to the value of model and the first argument set to 'z'.

bind 的一个很好的解释可以在 这里.

A good explanation of bind can be found here.

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