Create set of tests for new DB API

[Rjected]

Is your feature request related to a problem? Please describe.
Now that the database is refactored into something more logical, it would be useful to create a set of tests for the following APIs:

• SettlementEngine
• AuctionEngine
• LimitEngine
• AuctionOrderbook
• LimitOrderbook
• PuzzleStore
• DepositStore

Describe the solution you'd like
Each of the APIs are fairly descriptive, so creating tests for the API can serve as a test for all future datastore implementations. Creating inputs / outputs for each call is probably enough, given many of them are designed to have inputs as well as outputs.

Describe alternatives you've considered
The database implementations could also be tested individually, but this would probably be the same amount of work, except more useful.

Additional context
N/A