testing-characterization-test-generator

Characterization tests document the actual current behavior of existing code before refactoring, providing a regression safety net. You need them when modifying or modernizing legacy Swift codebases, especially before AI-assisted migrations, to ensure changes do not introduce unintended regressions.

To generate regression tests for legacy Swift code, describe the target module you want characterized. The generator identifies the public API surface, captures input and output behavior, and produces executable test templates through a discover, classify, generate, and verify methodology.

This characterization test generator works with any Swift project where you need to document existing behavior. It classifies the public API surface of your legacy codebase to produce executable templates, making it suitable for various Swift architectures preparing for code modernization.

Yes, you can use this to prepare an untested codebase for AI-assisted code migrations. It captures the current input and output behavior of your existing code and generates a regression suite, ensuring AI-assisted refactoring and modernization efforts do not break original functionality.

The best way to document current behavior for an untested Swift module is generating characterization tests. This approach identifies the public API surface, captures actual input and output behavior, and outputs executable templates with guidance to verify the regression suite.

When generating tests for legacy code, limitations include relying entirely on the visible public API surface rather than internal private implementations. The generated executable templates require manual verification to ensure the captured input and output behavior accurately reflects intended business logic.