The document discusses application architecture and describes layers, ports and adapters, and different types of testing. It explains that layered architecture helps define dependency rules and placement of components. Layers should only depend on deeper layers according to the dependency inversion principle. Ports define interfaces that external entities interact with, while adapters translate between ports and infrastructure. The document also outlines unit, integration, acceptance, and system tests and how to balance testing at different levels.

1. ADVANCED
APPLICATION
ARCHITECTURE
I - Layers
Matthias Noback
@matthiasnoback

2. matthiasnoback/layers-
ports-and-adapters-
workshop
Clone from GitHub
Follow the instructions in README.md

3. ARCHITECTURE
Decisions about coupling and cohesion

4. COUPLING
How are things linked to each other?

5. COHESION
Which things belong together?

6. COHESION
Which things belong together?
www.youtube.com/watch?v=N_7DPyxzUzc

7. LAYERED ARCHITECTURE
An answer to both questions

8. LAYERS
Help you protect what's in a deeper layer

9. LAYERS
Allow you to define dependency rules

10. LAYERS
Define the right place to put things

11. TRADITIONAL LAYERING
view
model
data

12. LAYERS
Horizontal division (as opposed to...)

13. USE CASES
Vertical division

14. LAYERS
Rendered as circles

15. CLEAN ARCHITECTURE
Or "union" architecture

16. COHESION
A basic set of layers
domain
application
infrastructure

17. COUPLING
The dependency rule
Layers should only depend on deeper layers

18. COUPLING
Dependency inversion principle
Classes should always depend on things that are more abstract

19. COUPLING
Dependency inversion principle
low-levelconcrete class specific
abstract interface generic high-level

20. COUPLING
Dependency inversion principle
use

21. COUPLING
Dependency inversion principle
use implement

22. COUPLING
Is about dependencies in code
Use Dependency Injection

23. LAYER CONVENTIONS
Domain layer
Domain model:
➤ Entities
➤ Value objects
➤ Domain services
➤ Factories
Business logic
Decisions
Data
State
Behavior

24. LAYER CONVENTIONS
Application layer
➤ Find an object
➤ Change something
➤ Notify something
➤ Get some information
Use cases
Orchestration

25. LAYER CONVENTIONS
Infrastructure layer
Communication with:
➤ HTTP client
➤ Database
➤ Filesystem
➤ Email server
➤ Message broker
Connecting the
application to
the world
outside

26. assignment/01.md
Layers

27. ADVANCED
APPLICATION
ARCHITECTURE
II - Ports & adapters

28. MESSAGING
... is the big idea

29. PORTS (COHESION)
Web, CLI, test client, messages, database queries
Web
Database

30. PORTS... AND ADAPTERS
Translation
HTTP
SQL

31. HEXAGONAL ARCHITECTURE
Same thing!
Web
Persistence

32. PORTS... AND ADAPTERS
(De)serialization, translation, structural validation
HTTP
SQL

33. assignment/02.md
Ports

34. PORT ADAPTERS
...in the Infrastructure layer

35. APPLICATION SERVICES
... in the Application layer

36. DOMAIN MODEL
in the Domain layer

37. APPLICATION SERVICES
Delivery-mechanism agnostic

38. assignment/03.md
Input adapters

39. VALIDATION
At different levels
Structural validation of messages
User-friendly input validation
Domain invariant protection

40. assignment/04.md
Input validation

41. APPLICATION SERVICES
Transactional consistency

42. assignment/05.md
Output adapter

43. assignment/06.md
A hidden dependency on the persistence mechanism

44. ADVANTAGES OF
PORTS & ADAPTERS
Offers insight into the application
Isolates the low-level details
Allows for alternative implementations
Helps with testing

45. ADVANCED
APPLICATION
ARCHITECTURE
III - Testing

46. UNIT TESTS
Testing your units of code
One class at a time
No IO
No setup required
Mocking only dependencies "you own"

47. INTEGRATION TESTS
Testing your adapters
Maybe multiple classes
Including IO
Some setup required
Mocking no dependencies

48. ACCEPTANCE TESTS
Testing your application services
Multiple classes
Use cases
Infrastructure stand-ins

49. SYSTEM TESTS
Testing your application end-to-end
The real deal

50. TESTING PYRAMID
Make it well-balanced
Unit tests
Integration tests
System
tests

51. assignment/07.md
Different types of tests

52. assignment/08.md
A test double for the Persistence port

53. assignment/09.md
An acceptance test for the application layer

54. A WELL-BALANCED TEST SUITE
Adapters can be easily replaced
Test suite is fast
Feedback is quick
Small amount of fragile tests
Enables continuous delivery