Computational notebooks are convenient for programmers, but can easily become confusing and inconsistent due to the ability to incrementally edit a program that is running. Recent reactive notebook systems, such as Ipyflow, Marimo and Observable, strive to keep notebook state in sync with the current cell code by re-executing a minimal set of cells upon modification. However, each system defines reactivity a different way. Additionally, within any definition, we find simple notebook modifications that can break each system. Overall, these inconsistencies make it difficult for users to construct a mental model of their reactive notebook's implementation. This paper proposes Rex, a fine-grained test suite to discuss and assess reactivity capabilities within reactive notebook systems. We evaluate Rex on three existing reactive notebook systems and classify their failures with the aims of (i) helping programmers understand when reactivity fails and (ii) helping notebook implementations improve.

翻译：计算笔记本对程序员而言十分便捷，但由于能够对正在运行的程序进行增量编辑，它们很容易变得混乱且不一致。近期的反应式笔记本系统，如Ipyflow、Marimo和Observable，致力于通过修改时重新执行最小单元格集合来保持笔记本状态与当前单元格代码同步。然而，每个系统对反应性的定义方式各不相同。此外，在任何定义下，我们都发现了可能破坏各系统的简单笔记本修改操作。总体而言，这些不一致性使得用户难以构建对其反应式笔记本实现的心理模型。本文提出Rex，一种细粒度测试套件，用于讨论和评估反应式笔记本系统中的反应性能力。我们在三个现有反应式笔记本系统上评估Rex，并对其故障进行分类，旨在（i）帮助程序员理解反应性何时失效，以及（ii）协助笔记本实现进行改进。