Designer spy using jasmine

Question

I want to look into the design function and tell how many times it was called using jasmine. I usually did something like this to set up an object method:

spyOn(lib,'methodName') 

but in the case when I try to look into the constructor actualy, so I tried:

 spyOn(lib); it('lib should be instantiated for each matching element', function () { spyOn(lib); expect(lib.calls.count()).toEqual(2); }); 

Unfortunately, this just gives me an error in the console:

 "Error: undefined() method does not exist in ..." 

How can I follow the constructor?

Answer 1

The spyOn() function can only replace the properties of an object, so the only thing you can do is keep an eye on the prototype. Now, if you follow the prototype of a real class, this will interfere with other tests, so you should use prototype inheritance.

You can do something like this:

 var mockClass = function (Subject) { var Surrogate = function () { Surrogate.prototype.constructor.apply(this, arguments); }; Surrogate.prototype = Object.create(Subject.prototype); Surrogate.prototype.constructor = Subject; return Surrogate; }; 

Some tests:

 var My = function (a) { this.init(a); }; My.prototype = { init: function (a) { this.setA(a); }, setA: function (a) { this.a = a; } }; var Mock = mockClass(My); spyOn(Mock.prototype, "constructor").andCallThrough(); spyOn(Mock.prototype, "init"); var m = new Mock(1); expect(Mock.prototype.init).toBe(m.init); expect(My.prototype.init).not.toBe(m.init); expect(m.constructor).toHaveBeenCalledWith(1); expect(m.init).toHaveBeenCalledWith(1); expect(ma).toBeUndefined(); m.setA(1); expect(ma).toBe(1); spyOn(Mock.prototype, "setA").andCallFake(function (a) { this.a = a + 1; }); m.setA(1); expect(m.setA).toHaveBeenCalledWith(1); expect(ma).toBe(2); 

You cannot keep an eye on constructor if your code uses type checking based on x.constructor . But I think this can only happen with the help of integration tests and poorly designed codes ...