How do you mock an angularjs $resource factory

I have a resource factory

angular.module('mean.clusters').factory('Clusters', ['$resource',
  function($resource) {
    return $resource('clusters/:clusterId/:action', {
        clusterId: '@_id'
    }, {
        update: {method: 'PUT'},
        status: {method: 'GET', params: {action:'status'}}
    });
}]);

and a controller

angular.module('mean.clusters').controller('ClustersController', ['$scope',
  '$location', 'Clusters',
    function ($scope, $location, Clusters) {
        $scope.create = function () {
            var cluster = new Clusters();

            cluster.$save(function (response) {
                $location.path('clusters/' + response._id);
            });
        };

        $scope.update = function () {
            var cluster = $scope.cluster;

            cluster.$update(function () {
                $location.path('clusters/' + cluster._id);
            });
        };


        $scope.find = function () {
            Clusters.query(function (clusters) {
                $scope.clusters = clusters;

            });
        };
}]);

I am writing my unit tests and every example I find is using some form of $httpBackend.expect to mock the response from the server, and I can do that just fine.

My problems is, when unit testing my controller functions I would like to mock the Clusters object. If I'm using $httpBackend.expect, and I introduce a bug in my factory every unit test in my controller will fail.

I would like to have my test of $scope.create test only $scope.create and not also my factory code.

I've tried adding a provider in the beforeEach(module('mean', function ($provide) { part of my tests but I cant seem to get it right.

I also tried

clusterSpy = function (properties){
    for(var k in properties)
        this[k]=properties[k];
};

clusterSpy.$save = jasmine.createSpy().and.callFake(function (cb) {
    cb({_id: '1'});
});

and setting Clusters = clusterSpy; in the before(inject but in the create function, the spy gets lost with

Error: Expected a spy, but got Function.

I have been able to get a spy object to work for the cluster.$update type calls but then it fails at var cluster = new Clusters(); with a 'not a function' error.

I can create a function that works for var cluster = new Clusters(); but then fails for the cluster.$update type calls.

I'm probably mixing terms here but, is there a proper way to mock Clusters with spies on the functions or is there a good reason to just go with $httpBackend.expect?