javascript - 如何测试对象的可选成员？

Question

测试可选对象成员的最佳技术是什么。现在我们在期望语句前面加上一个 if:

 if(object.member) expect(object).to.have.a.property('member').that.is.a('string');

但是必须有一种在风格上更加内联的方法。例如

 expect(object).to.have.an.optional.property('member').that.is.a('string');

或(为了便于阅读，添加为空链):

 expect(object).to.have.an.optional.property('member').that.would.be.a('string');

或者(移动可选以提供expect的替代版本):

 optionally.expect(object).to.have.a.property('member').that.is.a('string');

<小时/>

更新 - 我开始编写这段代码(chai 新手)，看看我是否可以实现我的目标，所以我添加了一个小插件:

module.exports = function(chai, utils) {
    var Assertion = chai.Assertion
        , i = utils.inspect
        , flag = utils.flag;

    var OPTIONAL_FLAG = 'chai-optional/option'
    Assertion.addProperty('optional', function() {
        flag(this, OPTIONAL_FLAG, true)
        return this;
    })

    Assertion.overwriteMethod('property', function (_super) {
        return function assertProperty (propertyName) {
            if (flag(this, OPTIONAL_FLAG)) {
                flag(this, OPTIONAL_FLAG, false) ;

                var obj = this._obj;
                var isPropertyPresent = (obj[propertyName]) ? true : false ;

                if(isPropertyPresent) {
                    return _super.apply(this, arguments);
                }

            } else {
                _super.apply(this, arguments);
            }
        };
    });

    Assertion.addProperty('would', function () {
        return this;
    });
};

使用情况:

it('could be null or have a value', function(done){
    var objWithout = {}
    var objWith = {}
    objWith.someProperty = 'blah'

    expect(objWith).to.have.optional.property('someProperty').that.would.be.a('string');
    expect(objWithout).to.have.optional.property('someProperty').that.would.be.a('string');

    return done();
})

当前的问题是，即使属性不存在，函数的控制也会结束 - 但评估链仍在继续。我需要在没有失败断言的情况下结束评估 - 这可能吗？

<小时/>

更新任一解决方案(简单的解决方案):

var either = function(firstCondition){
    var returnObject = {}

    try{
        firstCondition()
        returnObject.or = function(secondCondition){ return }
    } catch(e) {
        returnObject.or = function(secondCondition){ return secondCondition() }
    }
    return returnObject ;
}

module.exports = either

我认为实现有点笨拙 - 但粗箭头函数可能会削弱一些语法。所以就在这里等待!

Answer 1

The current problem even when the property isn't present, the control of the function ends - but the evaluation chain continues. I need to end the evaluation with out a failing assertion - is this possible?

在阅读了 chai 的 plugin 后guide我会使用类似的方法来设置标志。然而，我得出了同样的结论——你不能简单地停止一条链条。

我想到的一种可能性不仅是实现新属性和新标志，而且覆盖 assert方法本身 - 当 OPTIONAL_FLAG 时不抛出当前标记Assertion对象已设置。然而，破坏一切或错过边缘情况的机会太高。

毕竟，我认为这不是一个好主意。引用自this "confusing syntax" issue :

I think the misunderstanding comes from your expectation that Chai follows most/all English grammar rules. Unfortunately, English grammar has way too many rules (and exceptions to those rules) for it to be a reasonable undertaking to implement.

The challenge with designing Chai's chain-able assertions is finding the balance between being expressive and concise. Even if full grammar wasn't a daunting task to implement and document, it would make the API less concise, which is not good for a testing environment.

RULE: Any "flag" which modifies the behavior of an assertion (negation not or inclusion include/contain , etc...), once set to true should remain true until the end of the chain.

这意味着不可能实现像.or这样的东西。也是运算符。

但可能的是实现类似的东西

either(function(){
    expect(object).not.to.have.a.property('member');
}).or(function(){
    expect(object).to.have.a.property('member').that.is.a('string');
});

也许可以在此基础上构建一种更具吸引力的语法。