An outbox store in memory (tests; not durable).
Stores entry with the next entryId.
entry
entryId
The entry.
The stored entry.
Error when the key is already stored.
Error
Nothing to release.
Returns the failed entries in order.
The entries.
Changes the state of an entry; sent deletes it.
The new state.
Optional
The problem code of a failed entry.
Returns the pending entries in order.
An outbox store in memory (tests; not durable).