Write unit tests

We need unit tests that report coverage statistics.

The functionality that needs testing is described (at the WSAPI level) in Library Data Platform API

There are two fairly trivial calls to obtain information about the underlying database's schemas, tables and columns, and one call for searching. This is the only really interesting part of the module.

• The source-code is pretty short.

• It transforms JSON-structured queries into SQL. See the JSON schema for queries and an example query.

Testing these calls may involve mocking a back-end database. But much can be achieved just by testing the query translation. I will provide some example queries.

This issue was moved from: https://github.com/folio-org/mod-ldp/issues/18