[bm5k]

> Before running your test suite and checking everything is fine, the first thing you do is probably to look for the changelogs of updated gems.

Uh, no, the first thing you do is run the test suite.

[gkop]

Indeed. How about an analogous tool to the OP that uses binary search to deduce which updated gem(s) break the build, and then uses binary search on the intermediate versions of those gems to tell you exactly which version is the first bad one? Then spits out the changelog for that version ;)