Unit testing and mocking for cBots and Indicators

Is there a way to mock for example, the Bars property in a Robot, in order to write unit tests for a cBot or Indicator? I've been trying to use xUnit and NSubstitute to mock out Bars but I'm not really having any success at the moment.

I'm trying to mock parts of Bars, for example like so: 

var barSeriesMock = Substitute.For<Bars>();
barSeriesMock.Count.Returns(1000);

This doesn't seem to be working too well, so I must be doing something wrong. Is anyone aware if this is even possible?

I get the following errors when I try to access .Bars:

Object reference not set to an instance of an object.
  at cAlgo.API.Internals.Algo.get_MarketData()
  at cAlgo.API.Internals.Algo.get_Bars()

…surely, having mocked Bars, I should just get the mocked instance?