solid_skill

Overview

This skill transforms junior-level code into senior-engineer quality software by enforcing SOLID principles, test-first development, clean code, and pragmatic architecture. It is meant to be applied on every coding task—features, refactors, reviews, and debugging—to produce maintainable, testable, and change-resilient systems. The focus is practical: small, testable units, clear responsibilities, and incremental design through refactoring.

How this skill works

Start with failing tests (Red-Green-Refactor) and let design emerge during refactor steps. Apply the SOLID checklist to every class/module, wrap primitives in value objects, keep methods and classes tiny, and prefer abstractions over concretions. Use the provided code-smell triggers and pre/during/post coding checklists to guide decisions and stop to refactor when smells appear.

When to use it

• Writing new features or utilities
• Refactoring legacy or junior-written code
• Designing architecture or splitting modules
• Performing code reviews or QA handoffs
• Debugging production issues with long-term fixes

Best practices

• Always write a failing test first; follow Red-Green-Refactor
• One responsibility per class, methods <10 lines, max two instance variables
• Wrap domain primitives in value objects and prefer first-class collections
• Name things using domain language, consistent and specific
• Delay abstractions until the Rule of Three; avoid speculative generality

Example use cases

• Refactor a bloated service into smaller services and repositories with tests
• Convert primitive IDs and money values into validated value objects
• Design a vertical slice for a new feature with unit and integration tests
• Review a pull request and flag code smells such as long methods or primitive obsession
• Introduce dependency inversion to replace a concrete dependency with an interface for easier testing