使用 Jasmine 2 测试 Promise.then

Question

I have a function that is using a promise and calls another function when that promise fulfills. I'm trying to spy the function that executed in promise.then, however I can't get the expected calls.count() and I can't understand what I'm doing wrong.

var MyClass = function() {};

MyClass.prototype.doSomething = function(id) {
    var promise = this.check(id);

    promise.then(function(result) {
        this.make();
    });

    return promise;
};

MyClass.prototype.make = function() {};

describe('when', function() {
    var myClass;

    beforeAll(function() {
        myClass = new MyClass();
    });

    it('should', function(done) {
        spyOn(myClass, 'check').and.callFake(function() {
            return Promise.resolve();
        });

        spyOn(myClass, 'make');

        myClass.doSomething(11)
            .then(function() {
                expect(myClass.make.calls.count()).toEqual(1); // says it is called 0 times
                expect(myClass.check.calls.count()).toEqual(1); // says it is called 2 times
                done();
            });
    });
});

Answer 1

If your promise is compilant with the A+ spec then this:

promise.then(function(result) {
    this.make();
});

Will not work. As the spec requires this to have no value.

2.2.5 onFulfilled and onRejected must be called as functions (ie with no this value). [3.2]

Promises A+ 2.2.5

You'll need to do:

var that = this;
promise.then(function(result) {
    that.make();
});

Also, realize that the returned promise will try to fulfill or reject other queued promises at the same time as the promise returned by promise.then(..) unless you do:

promise = promise.then(..)

Answer 2

You have to respect the Promise chain by returning a promise in a promise

var that = this; // according to MinusFour answer
promise.then(function(result) {
   return that.make();
});

return promise;