codebase-design

A deep module in code design features a clean, minimal interface that conceals substantial implementation complexity. This structure enhances maintainability by reducing the surface area exposed to dependencies, making the codebase easier to test and modify without breaking calling components.

Assess module dependencies by categorizing them into in-process, local-substitutable, Ports & Adapters, and external categories. This dependency assessment clarifies how external interactions impact your code structure, guiding the specific deepening strategy needed for each module.

Place seams effectively at boundaries where dependencies require substitution for testing. Proper seam discipline separates interface from implementation, allowing you to replace rather than layer testing components, which ensures interface-driven tests remain robust.

The best way to test deep modules is using the 'replace, don't layer' approach. This strategy focuses on interface-driven testing, substituting dependencies directly through seams rather than adding complex test layers, ensuring tests remain maintainable.

Yes, you can use the Design It Twice technique to rethink a critical module's design. Analyze its current dependencies and seams, then explore alternative design improvements to achieve deeper, more testable code structures.

Deep module design may be unsuitable when an application demands extremely shallow, transparent pass-through logic where hiding implementation complexity behind a minimal interface would obscure critical data flow or introduce unnecessary abstraction layers.