测试一个由承诺返回的函数——检查错误

Question

我正在测试一个作为承诺的一部分返回的函数。我正在使用chai。

我可以测试该函数是否有效，但我无法测试它是否正确抛出错误。

我要测试的函数，省略了许多与承诺相关的代码:

// function that we're trying to test 
submitTest = (options) => {
  // missingParam is defined elsewhere. It works - the error is thrown if screenshot not passed
  if (missingParam(options.screenShot)) throw new Error('Missing parameter');
  return {};
}

我的测试:

describe('SpectreClient()', function () {
  let client;
  before(() => client = SpectreClient('foo', 'bar', testEndpoint));
  // the client returns a function, submitTest(), as a part of a promise
  /* 
  omitting tests related to the client
  */
  describe('submitTest()', function () {
    let screenShot;
    before(() => {
      screenShot = fs.createReadStream(path.join(__dirname, '/support/test-card.png'));
    });
    // this test works - it passes as expected
    it('should return an object', () => {
      const submitTest = client.then((response) => {
        return response.submitTest({ screenShot });
      });
      return submitTest.should.eventually.to.be.a('object');
    });
    // this test does not work - the error is thrown before the test is evaluated
    it('it throws an error if not passed a screenshot', () => {
      const submitTest = client.then((response) => {
        return response.submitTest({});
      });
      return submitTest.should.eventually.throw(Error, /Missing parameter/);
    });       
  });
})

测试的输出-

// console output
1 failing
1) SpectreClient() submitTest() it throws an error if not passed a screenshot:
   Error: Missing parameter

如何测试错误是否被正确抛出?我不确定这是摩卡的问题还是承诺的问题还是承诺的问题。非常感谢你的帮助。

Answer 1

承诺处理程序内部引发的异常被转换为承诺拒绝。submitTest在对client.then的回调中执行，因此它引发的异常成为承诺拒绝。

所以你应该这样做:

return submitTest.should.be.rejectedWith(Error, /Missing parameter/)