improve-codebase-architecture

Refactoring tightly-coupled code for testability involves finding deepening opportunities that turn shallow modules into deep ones. You consolidate complex logic behind a smaller interface, ensuring dependencies are categorized and replaced using real seams and adapter strategies.

Shallow modules are identified by interfaces that expose complexity and dependencies that are hard to test. Analyzing architectural friction reveals these shallow slices, where understanding behavior requires bouncing across many modules rather than leveraging a single deep interface.

Ports and adapters simplify dependency management by isolating remote-but-owned dependencies behind interfaces. This clarifies dependency categorization, ensuring true seams exist with two adapters rather than hypothetical ones, allowing behavior to change without editing in place.

Align testing strategy with refactoring by moving the test surface to the deepened module's interface. This replaces brittle shallow-module tests with interface-first testing discipline, leveraging the new deep modules to test behavior comprehensively.

Use dependency categorization when determining the safest deepening strategy across tightly-coupled systems. Classifying dependencies as in-process, local-substitutable, remote-but-owned, or true external guides how seams and adapters should be applied during refactoring.