It would be great to have a way to test the deck out within this application once a deck collection has been created. The functionality being requested is generally the same as what can be found from the following website: http://www.mtgdeckbuilder.net/Decks/EditDeck . The benefit to having similar functionality in this tool is that it would allow offline deck building and testing all in the same great tool. This deck testing tool would not have to deal with understanding the rules of the cards being played in any way; this feature would only need to be able to shuffle the deck, deal cards, keep track of cards that are in the library/graveyard/exiled groups (as well as those in play obviously), and allow for cards to be tapped and moved between these groups.
The above feature description attempts to match the functionality found at the website provided. One (potentially easy) additional feature to add would be to allow for two or more decks to go through this process at the same time. This would allow for testing out decks against each other.
The Graphics tab in the Deck view for each deck/collection (which is currently under construction) seems to go far towards enabling this type of behavior (from a visual standpoint).