Stubbing window.location.href with Sinon

Question

I am trying to test some client-side code and for that I need to stub the value of window.location.href property using Mocha/Sinon.

What I have tried so far (using this example):

describe('Logger', () => {
    it('should compose a Log', () => {
        var stub = sinon.stub(window.location, 'href', 'http://www.foo.com');
    });
});

The runner displays the following error:

TypeError: Custom stub should be a function or a property descriptor

Changing the test code to:

describe('Logger', () => {
    it('should compose a Log', () => {
        var stub = sinon.stub(window.location, 'href', {
            value: 'foo'
        });
    });
});

Which yields this error:

TypeError: Attempted to wrap string property href as function

Passing a function as third argument to sinon.stub doesn't work either.

Is there a way to provide a fake window.location.href string, also avoiding redirection (since I'm testing in the browser)?

Answer 1

You need to use global to mock the window object for your test in beforeEach or it

e.g.

it('should compose a Log', () => {
   global.window = {
       location: {
           href: {
               value: 'foo'
           }
       }
   }
  //.... call the funciton 
});

Answer 2

Stubs cannot replace attributes, only functions.

The error thrown reinforces this:

TypeError: Custom stub should be a function or a property descriptor

From the documentation:

When to use stubs?

Use a stub when you want to:

1. Control a method’s behavior from a test to force the code down a specific path. Examples include forcing a method to throw an error in order to test error handling.

2. When you want to prevent a specific method from being called directly (possibly because it triggers undesired behavior, such as a XMLHttpRequest or similar).

http://sinonjs.org/releases/v2.0.0/stubs/

---

Possible solution

While many builtin objects can be replaced (for testing) some can't. For those attributes you could create facade objects which you then have to use in your code and being able to replace them in tests.

For example:

var loc = {

    setLocationHref: function(newHref) {
        window.location.href = newHref;
    },

    getLocationHref: function() {
        return window.location.href;
    }

};

Usage:

loc.setLocationHref('http://acme.com');

You can then in your test write

var stub = sinon.stub(loc, 'setLocationHref').returns('http://www.foo.com');

Note the chained returns() call. There was another error in your code: the third argument has to be a function, not value on another type. It's a callback, not what the attribute should return.

See the source code of stub()