testability-patterns

name	testability-patterns
description	Implementation examples for the three testability rules (I/O isolation, pure logic, dependency direction) across Go, TypeScript, Python, Rust, and Dart. Loaded by reference from architectural-pattern.md — not triggered by file patterns.

Testability Patterns — Implementation Examples

Language-specific examples for the three testability rules defined in @.agents/rules/architectural-pattern.md. Load this skill when you need concrete implementation reference for I/O isolation, pure business logic, or dependency direction in a specific language.

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Rule 1: I/O Isolation — Interface + Adapter Pattern

Go

// storage.go — Contract defined in the consumer feature
type Storage interface {
    Create(ctx context.Context, task Task) error
    GetByID(ctx context.Context, id string) (*Task, error)
}

// storage_pg.go — Production adapter
type PostgresStorage struct{ db *sql.DB }

func (s *PostgresStorage) GetByID(ctx context.Context, id string) (*Task, error) {
    // real database query
}

// storage_mock.go — Test adapter
type MockStorage struct {
    tasks map[string]*Task
}

func (m *MockStorage) GetByID(ctx context.Context, id ) (*Task, ) {
    t, ok := m.tasks[id]
     !ok {
         , ErrNotFound
    }
     t, 
}