Kk db tests

[kevin-kline]

Description

This PR adds more model tests for domain layer entities.

Does this close any open issues?

related to (read for more details):

• https://github.com/merico-dev/lake/issues/972
• https://github.com/merico-dev/lake/issues/979

Other Information

Experiencing some unexpected behavior with migrations. Some result from "dirty database" problems:
https://github.com/golang-migrate/migrate/blob/master/FAQ.md#what-does-dirty-database-mean

[joncodo]

The way to fix the above error is documented in the Migrations.md file

## How to reset your DB. (https://github.com/golang-migrate/migrate/issues/282#issuecomment-530743258)

NOTE: Use this when you get an error like this "error: Dirty database version 16. Fix and force version."

1. Delete your DB
2. `migrate -path db/migration -database "mysql://root:admin@tcp(localhost:3306)/lake" -verbose force 1`
3. `migrate -path db/migration -database "mysql://root:admin@tcp(localhost:3306)/lake" -verbose down`
4. `migrate -path db/migration -database "mysql://root:admin@tcp(localhost:3306)/lake" -verbose up`