javascript - 如何使用 mocha、promise 和 catch block 防止误报

Question

我想利用 Mocha 内置的 Promise 支持，但当我想测试 Promise 链中的 catch 分支时，我很难处理误报。

This问题最接近我想要的，但解决方案要求我项目中的每个开发人员添加一个会引发错误的 then ，并确保该错误不会意​​外地通过测试。

因此，我不得不恢复使用 done 风格的测试，它依赖内置的超时来捕获错误而不是断言。这不太理想，但消除了误报的可能性。

var RSVP = require('RSVP');

function request (shouldSucceed) {
  if (shouldSucceed) {
    return RSVP.Promise.resolve('success');
  } else {
    return RSVP.Promise.reject(new Error('failure'));
  }
}

describe('request', function () {
  it('throws an error if shouldSucceed is not provided', function () {
    // this test is incorrectly calling `request`
    // which leads to it passing without actually testing
    // the behaviour it wants to
    return request(true)
      .catch(function (err) {
        expect(err).to.be.an.instanceof(Error)
      });
  });

  it('throws an error if shouldSucced is not provided (manual then block)', function () {
    // this test tacks a `then` onto the chain, to ensure `request`
    // actually throws an error as expected
    // unfortunately, it still passes since the assertion needs to do
    // a little extra work to ensure the type of error thrown is the
    // expected error
    return request(true)
      .then(function () {
        throw new Error('Not expected');
      })
      .catch(function (err) {
        expect(err).to.be.an.instanceof(Error)
      });
  });

  it('throws an error if shouldSucceed is not provided (done syntax)', function (done) {
    // this assertion fails (as it should)
    // due to a timeout
    return request(true)
      .catch(function () {
         expect(err).to.be.an.instanceof(Error);
         done()
      });
  });
});

输出:

  request
    ✓ throws an error if shouldSucceed is not provided
    ✓ throws an error if shouldSucced is not provided (manual then block)
    1) throws an error if shouldSucceed is not provided (done syntax)


  2 passing (2s)
  1 failing

  1) request throws an error if shouldSucceed is not provided (done syntax):
     Error: timeout of 2000ms exceeded. Ensure the done() callback is being called in this test.

是否有一种更简洁的方法来告诉 mocha 我期望在 catch block 中发生某些事情，并且成功解决 promise 应该是测试失败？

Answer 1

您正在寻找

it('request(false) should throw an error', function () {
    return request(false).then(function() {
        throw new Error('unexpected success');
    }, function(err) {
        expect(err).to.be.an.instanceof(Error)
    });
});

参见When is .then(success, fail) considered an antipattern for promises?获取与您当前代码的差异的解释。