Testing $httpBackend in Jasmine + Angular

I think I do everything the same way as in tutorials and there is weird bug. I want to mock $http in my LoginService and test it. Unfortunately there are some problems - it looks like it doesn't see $httpBackend functions. This is my LoginService:

app.factory('LoginService', function($http) {
//..
    var validateUser = function(username, password){
        $http.post('http://domain/api/login',
        {
            username: username,
            password: password
        })
        .success(function (data) {
            //...
        });
    };

    return {
        validateUser: validateUser,
        getLoginState: getLoginState
    };
});

And there is test for that validateUser function:

describe('LoginService', function() {
var httpBackend, LoginService;
beforeEach(module('app'));

beforeEach(inject(function ($httpBackend, _LoginService_) {
    LoginService = _LoginService_;
    httpBackend = $httpBackend;
}));

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

it('changes loginState object when user exists', inject(function(){
    data = {username: "ut_user", token: "123456"}; 
    httpBackend.expectPOST('http://domain/api/login').respond(data);
    LoginService.validateUser("user", "pass");
    httpBackend.flush();
    expect(LoginService.getLoginState().loggedIn).toBe(true);
}));
});

And there is error which was on httpBackend.verifyNoOutstandingExpectation(); and previously on httpBackend.flush():

ReferenceError: $ is not defined
//...
at Function.$httpBackend.verifyNoOutstandingExpectation (http://localhost:9876/base/node_modules/angular-mocks/angular-mocks.js:1563:38)
//...

I have in karma conf:

files: [
    'node_modules/angular/angular.js',
    'node_modules/angular-*/angular-*.js',
    'js/**/*.js',
    'spec/**/*.js'
],