Blockchain tests are found int /BlochchainTests The Goal for theses tests is to see if the clients can correctly process a blockchain. Some of the tests contain invalid blocks. In those case clients should only add the valid blocks to their blockchains.

{
  "lastBlock": "..",
  "blockchain": []
}

lastBlock contains the hash of the last valid block in the chain.
blockchain A sequential list of blocks.

getting the blocks for blockchain was by installing edt and running bcm export -c which will dump cpp-ethereum's current blockchain.