BitcoindComparisonTool.jar is a tool that uses the bitcoinj library to generate very-low-difficulty blockchains that test edge-cases in block chain logic. Full implementations of the Bitcoin protocol can use it to help test that their logic for handling valid/invalid blocks matches the reference implementation. Improvements are welcome; the source code used to generate the blocks is in FullBlockTestGenerator.java. The source that drives the tool can be found at https://github.com/TheBlueMatt/bitcoinj/blob/blocktester/core/src/test/java/org/bitcoinj/core/BitcoindComparisonTool.java