Applicative Architecture

Test-Driven Development — red/green/refactor as a design discipline, not just a testing technique.

Behavior-Driven Development — specifying behavior in shared language (Given/When/Then) and driving development outside-in.

Domain-Driven Design — modeling software around the business domain, with a ubiquitous language and explicit bounded contexts.

Behavior-preserving code transformations — the catalog, the smells that trigger them, and how to refactor safely.

Principles for readable, maintainable code — naming, small functions, SOLID, and the debates around the canon.

Ports & adapters — isolating the domain from infrastructure so the application is testable and technology-agnostic at its edges.

Why the house layout starts as a modulith and how its in-process service seam turns the move to microservices — and back — into a wiring change rather than a rewrite.

What each language buys and pays for the same architectural property — that a bounded context can be carved out as a wiring change — graded by what genuinely enforces each wall, with the findings that only a compiler revealed.

Separating writes from reads, and storing state as a log of events — two distinct patterns, their real costs, and when each earns its keep.

The GoF catalog read critically — which patterns still matter, which dissolved into languages, and the modern vocabulary that replaced the rest.

Design rules for scaffolders, provisioners and any tool that writes files another tool consumes — render the native format, delegate the doing, never offer a partial answer, and make the record the source of truth.

ADRs for decisions, the C4 model for structure — lightweight documentation that stays true because it's cheap to keep.

Testing as a strategy, not a ritual — the pyramid and its critics, contract and property-based testing, load and chaos, and testing in production.

The two forces every architecture balances — minimize how much modules know about each other, maximize how much each module belongs together.

Which direction subtyping flows through generics and function signatures — and how variance is Liskov substitution formalized, with interface segregation as its enabler.

Practice material for the theme's concepts — katas, challenges, and multi-milestone build projects.