testing-patterns

Seams and dependency injection break tight coupling. Seams let you intercept behavior at specific points—through method parameters, extracted interfaces, or wrap method patterns—without modifying production code, enabling you to inject test doubles and isolate units for testing.

Characterization tests document actual system behavior before refactoring. Write them to capture current output, then use them as a safety net while refactoring. They're essential when you lack a test suite and need confidence that changes don't alter external behavior.

Apply safe refactoring techniques: identify pinch points and interception points in your codebase, use sprout methods to extract logic incrementally, and rely on characterization tests as your safety net. These patterns guide structural changes while maintaining behavior across languages like TypeScript.

Test doubles (stubs, mocks, fakes) replace real dependencies during testing. Stubs return fixed values, mocks verify calls were made, fakes provide working implementations. Choose based on what you need to isolate: use stubs for read-heavy dependencies, mocks for behavior verification, fakes for stateful interactions.

Yes. Seams, test doubles, dependency injection, and safe refactoring patterns are language-agnostic principles. The Skill covers applications in TypeScript and other languages, adapting technique names and syntax while preserving the core strategy for improving testability and enabling confident refactoring.

Locate pinch points—narrow sections where many dependencies flow through—and interception points where you can inject test doubles. Use wrap method patterns to intercept calls incrementally. Sprout methods extract testable logic without rewriting entire modules, prioritizing high-impact areas first.