Implement Shopping Cart UseCase: Checkout-Shopping-Cart, Case 1

Context

we made preparations and now time for first business flow implementation
Take a look on 1-documentation/business/shopping-cart/Checkout-Shopping-Cart.md for general overview of flow
Remember about SOLID, KISS, DRY, OOP, Hexagonal Architecture
Remember about Reactiveness
Remember that database, rest controller, order service return the Flux/Mono objects

Acceptance Criteria

Defined interface for communication with Database (not implementation!)
Defined only necessary methods for communication with Database in scope of task
Defined interface for communication with Order Service (not implementation!)
Implemented Validate Shopping Cart functionality (consider using GoF patterns, e.g. Chain of Responsibility or Strategy)
Partially implemented Shopping Cart UseCase: Case 1 (without database, rest, order service communications)
Covered with unit tests: UseCase, Validation Shopping Cart
Implemented all mapping through Mapstruct
Fell free to add any DTOs that improve readability

Technical Details

Be align with Testing Agreement described in Working-Agreement.md
Be align with Common Architectural Agreement described in Working-Agreement.md
Be sure of using StepVerifier for reactive unit test (https://medium.com/digitalfrontiers/step-up-your-reactive-tests-with-the-stepverifier-126654fbcdef)

sokimaaa / 6Core