Hm, I've never used this feature (nor did I even know it existed until now), but looking at the source, it looks like it works this way. In the directory pkg:/csfake, you can have these xml files:
CheckOrder.xml
PlaceOrder.xml
GetCatalog.xml
GetPurchases.xml
GetUpgrade.xml
UpgradeChannel.xml
If you call roChannelStore.FakeServer(true), then the response to a channel store request will be the contents of the corresponding xml file. No transaction with the channel store actually takes place.
--Mark