angular2 testing: add latency to mock http backend - unit-testing

Question

I have a service that gets data from two different backends (database over http request and live data over socket.io) and then publishes this data as a single stream. When testing this service, I would like to be able to control the delay of the mock http service, so that I can play through different kinds of racing conditions. Currently I'm doing this:
beforeEach(() => {
TestBed.configureTestingModule({
providers: [
DataService,
{
provide: IoService,
useClass: MockIoService
},
{
provide: Http,
useFactory: (mockBackend, options) => {
return new Http(mockBackend, options);
},
deps: [MockBackend, BaseRequestOptions]
},
MockBackend,
BaseRequestOptions
]
});
});
it('should get data from http backend', async(inject([DataService, MockBackend, IoService], (service: DataService, mockBackend, ioService) => {
const mockResponse = {
data: [
{ id: 0, text: 'httpData', start: 0, stop: 1 }
]
};
mockBackend.connections.subscribe((connection) => {
connection.mockRespond(new Response(new ResponseOptions({
body: JSON.stringify(mockResponse)
})));
});
service.subscribe('test').subscribe((data) => {
expect(data.text).toBe('httpData');
});
})));
This works but again, I would like to be able to define a delay for the MockBackend so that the response comes after a fixed number of seconds. Is that possible and if yes, how?