# Functions
AcceptanceTest is the acceptance test that all implementations of DB should pass.
ContextWithTransaction wraps ctx and returns a context that contains transaction.
TransactionFromContext fetches the transaction from the context.
# Variables
ErrKeyNotExist is returned from DB.Get when retrieving a non-existing key.
# Interfaces
DB defines the interface for a key-value store.
Transaction defines the interface for an isolated ACID DB transaction.