gistfile1.js

/*
 We have two classes: resultRenderer and dbQuery
 resultRenderer will ask dbQuery to perform a database query, and asyncronously receives the results
*/

function resultRenderer(query) { this._query = query }

resultRenderer.prototype = {
	queryResultsAndRender: function () {
		this._query.runQueryAsync(this.renderResults.bind(this));
	},
	
	renderResults: function (results) {
		// now render them!
	}
}

function dbQuery() {}
dbQuery.prototype = {
	runQueryAsync: function (callback) {
		// query the database, and callback once we have results:
		callback(queryResults);
	}
}

// to test resultRenderer using a mocked dbQuery, we write something like:

query = new dbQuery;
fakeResponse = { some: "reasonable data"}
spyOn(dbQuery, 'runQueryAsync').andCallFake(function(callback) {
        callback(fakeResponse);    
});
renderer = new resultRenderer(query);
spyOn(renderer, 'resultsRenderer');
renderer.queryResultsAndRender();

//two options here: 

//1) expect that our callback got the right args, unit test callback with another spec. 
expect(renderer.resultsRenderer).to.haveBeenCalledWith(fakeResponse);

//2) test the result of our callback getting the args. 
expect(someOtherThingThatsTheResultOfOurRenderer).toBe(inTheDOMEtc);

@ragaskar

How would we test the case where I have a function that calls a service that performs an ajax call. I pass the service function a parameter and a callback. How would I mock the calling of that callback function and test the parameters in which the original service function was called with. For example, here is the function we want to test

$scope.destroy = function(comment) {
    Comment.remove({id: comment.id}, function() {
        $scope.comments = _.without($scope.comments, comment);
    })
};

I want to test that Comment.remove is called with an object and a callback function. Then I want to test the functionality of that callback function (e.g. an element being removed from $scope.comments).

Any suggestions