Ultraprune This switches bitcoin's transaction/block verification logic to use a "coin database", which contains all unredeemed transaction output scripts, amounts and heights. The name ultraprune comes from the fact that instead of a full transaction index, we only (need to) keep an index with unspent outputs. For now, the blocks themselves are kept as usual, although they are only necessary for serving, rescanning and reorganizing. The basic datastructures are CCoins (representing the coins of a single transaction), and CCoinsView (representing a state of the coins database). There are several implementations for CCoinsView. A dummy, one backed by the coins database (coins.dat), one backed by the memory pool, and one that adds a cache on top of it. FetchInputs, ConnectInputs, ConnectBlock, DisconnectBlock, ... now operate on a generic CCoinsView. The block switching logic now builds a single cached CCoinsView with changes to be committed to the database before any changes are made. This means no uncommitted changes are ever read from the database, and should ease the transition to another database layer which does not support transactions (but does support atomic writes), like LevelDB. For the getrawtransaction() RPC call, access to a txid-to-disk index would be preferable. As this index is not necessary or even useful for any other part of the implementation, it is not provided. Instead, getrawtransaction() uses the coin database to find the block height, and then scans that block to find the requested transaction. This is slow, but should suffice for debug purposes.

The sources in this directory are unit test cases.  Boost includes a
unit testing framework, and since bitcoin already uses boost, it makes
sense to simply use this framework rather than require developers to
configure some other framework (we want as few impediments to creating
unit tests as possible).

The build system is setup to compile an executable called "test_bitcoin"
that runs all of the unit tests.  The main source file is called
test_bitcoin.cpp, which simply includes other files that contain the
actual unit tests (outside of a couple required preprocessor
directives).  The pattern is to create one test file for each class or
source file for which you want to create unit tests.  The file naming
convention is "<source_filename>_tests.cpp" and such files should wrap
their tests in a test suite called "<source_filename>_tests".  For an
examples of this pattern, examine uint160_tests.cpp and
uint256_tests.cpp.

For further reading, I found the following website to be helpful in
explaining how the boost unit test framework works:

http://www.alittlemadness.com/2009/03/31/c-unit-testing-with-boosttest/