Issue #92: Improve test coverage

.gitlab-ci.yml

config/ci_database_test.env.example

config/ci_monet_test.env.example

config/ci_postgres_test.env.example

config/ci_test.yaml.example

config/market_dimensions.yaml.example

config/market_enum.yaml.example

config/market_views.yaml.example

config/source_test_only.yaml.example

config/test/postgres/fixtures/sellerstatus.json

src/adapter/monet.ts

src/adapter/postgres.spec.ts

src/adapter/postgres.ts

src/api/controllers/collect.spec.ts

src/api/controllers/collect.ts

src/api/controllers/data.spec.ts

src/api/controllers/engine.spec.ts

src/api/middlewares/error.spec.ts

src/core/adapter.ts

src/core/engine.spec.ts