GetProcessor returns a Processor associated with the txType.

Initialize sets the custom processors.

InitializeTestEnv initializes custom tx processors for test.

InvalidTxError is expected to be thrown by a custom transaction processor (an implementation of interface `Processor`) if it wants the ledger to record a particular transaction as invalid.

Processor allows to generate simulation results during commit time for custom transactions.

Processors maintains the association between a custom transaction type to its corresponding tx processor.