"使用 Jasmine 进行单元测试，模拟构造函数"

Question

I'm unit testing JavaScript with Jasmine and I am running into some problems.

var layers = new Layers()

Answer 1

IMO, it's unnecessary to spy on window , since you can easily shadow the variable in local scope by creating a spy object with the same name:

describe('Map', function () {
    var Layers;

    beforeEach(function () {
        Layers = function () {
            // alternatively, you could move this to Layers.prototype
            this.addLayers = jasmine.createSpy('Layers#addLayers');
        };
    });

    /* ... */
});

If you want an automatic mocking and using CommonJS modules, you may try Jest framework, which is built on top of Jasmine.

Answer 2

Let's talk in terms of example classes you have provided.

You're writing a test suite for Map . All its dependencies (in example we have only Layer ) MUST be mocked. Because in a unit test you're supposed to test one layer, as small functionality as possible. It means that you should provide such a mocked Layer constructor that exposes interface used in Map . For example:

function Layers() {
    this.addLayer = sinon.spy();
}

In this test suite only Map class should remain "real". Ie it's code must not be altered. And with such mockups like Layer you make sure that you do not trigger any interaction with real-code dependencies (own-written dependencies should be tested in a different test suite, also make sure you don't try to test framework functions, like $tate.resolve , $inject etc.). If class Map is complicated and has multiple dependencies, investigate sinon features that help automate this process, for example sinon.mock

Answer 3

If you ever transpile class syntax to a es3 or another pre-2015 dialect you will discover something interesting.

class a {
    constructor(){
        ...
    }
    
    index()
   {
      ...
   }
}

Becomes:

var a = /** @class */ (function () {
    function a() {
        ...
    }
    a.prototype.index = function () {
       ...
    };
    return a;
}());

This same implementation is used by later standards but masked by the 2015 class syntax. In other words a.index doesn't exist instead it's defined as a.prototype.index . Thus you need spyOn(a.prototype, 'index') to spy on it.

Change spyOn(Layers, 'addLayer') to spyOn(Layers.prototype, 'addLayer')