$httpBackend is one of the greatest things that AngularJs provides. $httpBackend intercepts AJAX requests made by Angular's $http service to allow for full unit testing. The ngTestHarness helps simplify interactions with the mock backend by abstracting away WHEN and EXPECT differences.
This is the first time I can point to open source code that I took a large part in authoring. I am proud of the project that the very talented Team Titan at Gaikai, a Sony Entertainment Company, has created. While updating/adding unit tests for development and build purposes we became very disenchanted with the complexity required for creating unit tests in Angular.