Javascript Chai expect.to.throw错误不相等

我试图使用expect断言抛出特定错误

已成功捕获错误，但错误比较失败。这包括thrownCustomError和new CustomError以及thrownCustomError和customErrorInstance。然而，似乎使用expect.to.throwCustomError“自定义错误”确实有效

在我的例子中，我特别希望断言使用参数生成错误消息的自定义错误，因此使用后一种比较相当麻烦

我做错了什么？非常感谢您的建议

let chai = require("chai");
const expect = chai.expect;
const assert = chai.assert;

class CustomError extends Error{
    constructor() {
        super('Custom error')
    }
}

const throwFn = () => {
    throw new CustomError()
}

const customErrorInstance = new CustomError()

describe('CustomError Test', () => {
    it('should throw a CustomError (new)', () => {
        expect(throwFn).to.throw(new CustomError())
    })

    it('should throw a CustomError (const)', () => {
        expect(throwFn).to.throw(customErrorInstance)
    })

    it('should produce a strictly equal error', (done) => {
        try {
            throwFn()
        } catch (e) {
            assert(e === new CustomError(), 'Thrown error does not match new instance of error')
            assert(e === customErrorInstance, 'Throw error does not match const instance of error')
            done()
        }
        expect.fail()
    })
})

输出：

  CustomError Test
    1) should throw a CustomError (new)
    2) should throw a CustomError (const)
    3) should produce a strictly equal error


  0 passing (38ms)
  3 failing

  1) CustomError Test
       should throw a CustomError (new):

      AssertionError: expected [Function: throwFn] to throw 'Error: Custom error' but 'Error: Custom error' was thrown
      + expected - actual


      at Context.it (test.js:19:27)

  2) CustomError Test
       should throw a CustomError (const):

      AssertionError: expected [Function: throwFn] to throw 'Error: Custom error' but 'Error: Custom error' was thrown
      + expected - actual


      at Context.it (test.js:23:27)

  3) CustomError Test
       should produce a strictly equal error:
     AssertionError: Thrown error does not match new instance of error
      at Context.it (test.js:29:4)

---

您每次都在测试实例，因此需要使throwFn抛出该实例：

const customErrorInstance = new CustomError()

const throwFn = () => {
    throw customErrorInstance
}

// should throw a CustomError (const)
expect(throwFn).to.throw(customErrorInstance);

第一个测试，您必须更改为类，因为您在函数中抛出一个单独的实例，然后尝试与expect中的一个新实例进行比较，这永远不会是真的，根据定义，一个实例并不严格等同于另一个实例：

const throwFn = () => {
    throw new CustomError()
}

expect(throwFn).to.throw(CustomError)

因为您所做的是尝试通过执行expectthrowFn.to.thrownew CustomError来比较实例，所以这将永远不会成功

这是你的代码

---

经过深入挖掘，柴对误差相等性的评价似乎是。。。奇怪的错误由消息和堆栈跟踪组成。由于堆栈跟踪因错误实例化的位置而异，因此如果不抛出相同的实例，expect.to.throw中就无法实现相等

我能找到的唯一只会断言错误消息的解决方案如下：

const a = new CustomError()
...
it('should produce a strictly equal error', (done) => {
    try {
        throwFn()
    } catch (e) {
        assert(e.message === a.message, 'Thrown error does not match new instance of error')
        done()
    }
    expect.fail()
})

---

注意：在撰写本文时，有一个公开的PR来删除/修改此行为

感谢您的回复，但这并不是一个实际的解决方案。除了幼稚的例子之外，人们怎么能期望能够指定抛出错误的实例呢？如上所述，我希望验证传递给错误构造函数的参数。考虑一个预期的：X获取：Y错误格式。我需要验证x和x的值y@DAnsermino是的，我们不应该测试错误的实例，我们应该检查类型，就像我如何修复您的第一个示例-expectthrowFn.to.throwCustomError。如果要对消息进行asserton，则传入一条消息expectthrowFn.to.throwCustomError，/应包含以下内容/

const a = new CustomError()
...
it('should produce a strictly equal error', (done) => {
    try {
        throwFn()
    } catch (e) {
        assert(e.message === a.message, 'Thrown error does not match new instance of error')
        done()
    }
    expect.fail()
})