Unknown Provider Error while trying to test generic angularjs $resource service

I have generic service that create resources for my application:

(function(module) {
module.provider('restService', {

    resourceRegistry: {},
    addRestResource: function(entityName, entityProto) {
        this.resourceRegistry[entityName] = entityProto;
    },

    $get: function() {
        var restService;
        for (var entityName in this.resourceRegistry) {
            createRestResource(entityName, this.resourceRegistry[entityName]);
        };

        restService = {
            //createRestResource: createRestResource
        };

        return restService;
  }});

  function createRestResource(entityName, entityProto) {
    console.log('registering model: ' + entityName);
    module.provider(entityName, { $get: function($resource, $http) {
        var resource = $resource('/api/' + entityName + '/:id', { // TODO use config
            id : '@id' //this binds the ID of the model to the URL param
        },{
            query : { method : 'GET', isArray : true }, //this can also be called index or all
            update : { method : 'PUT' },
            create : { method : 'POST' },
            destroy : { method : 'DELETE' }
        });

        // here gose some other functionality unrelated to the topic...

        return resource;
    }});
}}(angular.module('restService', ['ngResource'])));

I can be used by any other module using

module.config(['restServiceProvider', function(restServiceProvider) {
  restServiceProvider.adRestResource('User', { name: null, email: null });
}

And while above actually works for me in the application I cannot get working jasmine/karma test for it. The problem is that trying various method to configure restServiceProvider I always end with error stating that for eg TestEntity there is unknown provider TestEntityProider. Although I have tried different approaches to configure the resourceRegistry before the resource is being created, here is some test file.

describe('testing restService', function () {
    var httpBackend;
    var theRestServiceProvider;

    beforeEach(function() {
        module('ngResource');
        module('restService');
        var fakeModule = angular.module('test.app.config', ['ngResource'], function () {});
        fakeModule.config( function (restServiceProvider) {
            theRestServiceProvider = restServiceProvider;
            restServiceProvider.addRestResource('TestModel', {testProp: null});
        });

        module('test.app.config');
    });

    beforeEach(function () {
        inject(function ($httpBackend) {
            httpBackend = $httpBackend;
        })
    });

    beforeEach(inject(function (restService) {}));



    describe('create restService entity', function() {
        it('should post entity with nonempty testProp',
            function() {
                theRestServiceProvider.addRestResource('TestModel', {testProp: null});

                inject(function(TestModel) {
                    var object = new TestModel();
                    object.testProp = 'John Doe';

                    httpBackend.expectPOST(/.*/,
                        function(postData) {
                            console.log("post data: " + postData);
                            jsonData = JSON.parse(postData);
                            expect(jsonData.testProp).toBe(object.testProp);

                            return jsonData;
                        }).respond({});

                    var response = object.$create();

                    httpBackend.flush();
                });
            });
    });
});

IMO this is because within the test the registering resource is being done 'too late' but still I don't know how to do this right.