Show HN: RealDiff – runtime behavior diffing for pull requests (six languages)
RealDiff is a tool designed to detect runtime behavior changes in code that standard source diffs might miss. It works by running tests across different Git revisions to identify functional discrepancies, even in files not directly modified by a pull request.
Why it matters
It helps developers prevent unintended side effects in complex software systems, reducing the risk of bugs in production environments.
RealDiff finds runtime behavior changes that ordinary source review misses .
It builds two Git revisions, observes their tests, learns a noise baseline from three base runs, and reports the first changed behavior in each call tree. A source diff tells you what was edited. RealDiff tells you what the edit did, including effects in files the pull request never touched.
A harmless-looking refactor can change behavior far from the edited file:
public static List<(int Priority, T Value)> ByPriority<T>( - this IEnumerable<(int Priority, T Value)> src) - { - var list = src.ToList(); - list.Sort((a, b) => a.Priority.CompareTo(b.Priority)); - return list; - } + this IEnumerable<(int Priority, T Value)> src) => + src.OrderBy(item => item.Priority).ToList(); List.Sort is not stable; OrderBy is. In the included demo, that one-line infrastructure change alters an unedited pricing engine:
Get smarter about the news
Sign up free for a feed built around what you actually care about, Dive Deeper research on any story, and the full text of every article.
Create free accountAlready have an account? Sign in