What problem does it solve? Legacy or tightly-coupled code often cannot be tested because functions directly construct collaborators, call static or global functions, or reach external systems without any substitution point. This Skill guides you to find and introduce seams — places where behavior can be altered without editing the call site — so existing behavior can be placed under test. ## Core Features & Use Cases - Seam Identification: Locates existing seams in function parameters, default values, module imports, configuration, React props/context, and hard-coded dependencies. - FP-First Seam Creation: Provides TypeScript techniques including parameter injection with production defaults, higher-order function factories, narrow type extraction, and wrapping global calls like Date.now() or process.env. - Legacy OOP Patterns: Covers extract-and-override and constructor injection for class-based code, with a migration path toward functional parameter injection. - Use Case: You need to test a scheduleDelivery function that calls an external transit API directly. The Skill shows how to add a resolveTransitDays parameter with a production default, letting tests pass a fake while production call sites stay unchanged. ## Quick Start Ask the assistant to find seams in a tightly-coupled TypeScript function so it can be tested without hitting its real external dependencies.
