angular unit testing advice

I'm new to unit testing with Angular and I'm having a great deal of trouble even getting starting with the testing. I have a controller that calls a service that calls a remote api to get a list of currencies, and then augments the returned object with a symbol property and assigns it to a scope variable.

I've been looking at a lot of httpBackend tutorials but the pieces aren't fitting together. I know I have to use whenGet and expectGet but still don't understand what they are and when I should use them, or even what I should be testing - the request, the response? Should they be in the beforeEach function of the it function?

the controller:

whiskyControllers.controller('currencyCtrlr', ['$scope', 'CurrencyConversion', 'UpdateMiniBasket', 'whiskyList',
    function($scope, CurrencyConversion, UpdateMiniBasket, whiskyList){

        $scope.getCurrencies = function(e){
            e.preventDefault();

            CurrencyConversion.async().then(function(d) { 

                $scope.rates = d.data.rates;

                for(var i = 0, j = $scope.rates.length; i < j; i++){
                    $scope.rates[i]['symbol'] = insertSymbol($scope.rates[i].to);
                }
            });
        }
}]);

I've copied the bulk of the test below from another tutorial but it still fails with 'Error: No pending request to flush'

the test:

describe('currencyCtrlr: getCurrencies', function() {
    var scope, CurrencyConversion, UpdateMiniBasket, whiskyList, $httpBackend, $rootScope, createController,
        url = 'http://ift.tt/1D4B8HL';

    beforeEach(module('whiskyControllers'));

    beforeEach(function () {
        module(function ($provide) {
            $provide.value('CurrencyConversion', CurrencyConversion);
            $provide.value('UpdateMiniBasket', UpdateMiniBasket);
            $provide.value('whiskyList', whiskyList);
        });
    });

    beforeEach(inject(function($injector) {
        //scope = $rootScope.$new();
        $httpBackend = $injector.get('$httpBackend');
        $httpBackend.when('GET', url).respond({}, {});

        $rootScope = $injector.get('$rootScope');
        var $controller = $injector.get('$controller');

        createController = function() {
            return $controller('currencyCtrlr', {'$scope' : $rootScope });
        };
    }));

    it('should make an ajax call to http://ift.tt/1EoBq0B', function() {
        $httpBackend.expectGET(url);
        var controller = createController();
        $httpBackend.flush();
    });

    afterEach(function() {
        $httpBackend.verifyNoOutstandingExpectation();
        $httpBackend.verifyNoOutstandingRequest();
    });

});

Any help will be really appreciated