Introduction into testing

Litte golang api server with broken architecture and no tests. It'll become better over iterations.

How to run

go run cmd/main.go --conf=conf.yaml

Chapters

• v0.0.1: added some unit tests, fixed bug in GET /orders and decouple pool&repo from usecase.
• v0.0.2: added intergration tests for gateway-usecase layers. Also added tests with fakes.