Chrysalis: A Lightweight Logging and Replay Framework for Metamorphic Testing in Python

Metamorphic testing (MT) is a powerful technique for software testing. We introduce Chrysalis, a lightweight, extensible logging and replay-based metamorphic testing framework in Python. Chrysalis allows developers to define custom input transformations and their associated invariants, then execute structured metamorphic testing campaigns. Its key innovation is a lightweight logging mechanism that records the full history of transformations applied to an input. This compact representation enables developers to not only identify test failures but also to replay the exact sequence of transformations leading to a bug, facilitating debugging. We demonstrate Chrysalis’s effectiveness through two case studies: auditing a machine learning model for fairness and assessing the robustness of large language models.A screencast demonstrating Chrysalis is available at: https://youtu.be/xJG4qghxlIs, and the source code is available at: https://github.com/Chrysalis-Test/Chrysalis.