public void IsSingleMoveDownValid()
{
INextValueGenerator <sbyte> generatorMock = MockRepository.GenerateStub <INextValueGenerator <sbyte> >();
generatorMock.Stub(m => m.NextPosition(Arg <sbyte> .Is.Anything)).Return(0); //put initial value to cell "0" [0,0]
generatorMock.Stub(m => m.NextValue()).Return(2); //cell Value shall be 2
IGameBoard board = InitBoard(4, generatorMock);
board.MoveDown(); //Now cell [3,0] must contains 2
Assert.AreEqual(board.To2DArray()[board.Size - 1, 0].Value, 2);
}