如何使用 mocha、chai 和 sinon 证明调用实现回调？答案

【问题标题】：How can one prove the invocation of fulfillment callback using mocha, chai and sinon?如何使用 mocha、chai 和 sinon 证明调用实现回调？
【发布时间】：2018-02-23 10:31:40
【问题描述】：

考虑以下 mocha+chai+sinon 测试：

it("will invoke the 'then' callback if the executor calls its first argument", function(done){
    let executor = function(resolve, reject){
        resolve();
    }
    let p = new Promise(executor);
    let spy = sinon.spy();

    p.then(spy);

    spy.should.have.been.called.notify(done);
});

如断言中所述，我预计应该调用 spy。但是，mocha 报告：

1) A Promise
   will invoke the 'then' callback if the executor calls its first argument:
    AssertionError: expected spy to have been called at least once, but it was never called

用 console.log 替换 spy 展示了预期的流程，所以我对 mocha 报告否定的原因感到困惑。

如何更改测试以证明预期的行为？

【问题讨论】：

标签： mocha.js chai sinon-chai

【解决方案1】：

我发现解决方法是使用async/await，如下：

it("will invoke the 'then' callback if the executor calls its first argument", async() => {
    let executor = function(resolve, reject){
        resolve();
    }
    let p = new Promise(executor);
    let spy = sinon.spy();

    await p.then(spy);

    spy.should.have.been.called;
});

【讨论】：

【解决方案2】：

实现相同目的的另一种方法是：

it("will invoke the 'then' callback if the executor calls its first argument", function(){
    let p = new Promise(function(resolve, reject){ resolve(); });
    let resolver = sinon.spy();

    p.then(resolver);

    return p.then( () => { resolver.should.have.been.called; });
});

【讨论】：