Issue #20871 has been updated by sanderd17 (Sander Deryckere). Forgot to mention. We use the `parallel_tests` gem to speed up our specs in CI. On my local environment, with synchronous tests, I haven't been able to reproduce the same behaviour either. ---------------------------------------- Bug #20871: Including methods in Enumerable doesn't make them available in Array https://bugs.ruby-lang.org/issues/20871#change-110416 * Author: sanderd17 (Sander Deryckere) * Status: Open * ruby -v: 3.3.6 * Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN ---------------------------------------- Today, our CI pipeline started failing after the automatic update from v3.3.5 to v3.3.6. After researching, it turned out that our core extensions to the `Array` class weren't loaded anymore. The core-extensions code looks like this: ```ruby module CoreExt module Enumerable def average sum(&:to_f) / count if any? end # def ... end end Enumerable.include CoreExt::Enumerable ``` After some debugging, it turned out that the `average` method was included in the `instance_methods` of `Enumerable`, but not in the `instance_methods` of `Array`. Explicitly adding `Array.include CoreExt::Enumerable` fixes CI for our case. The very strange thing is that it only happens on a release branch we are still maintaining. It doesn't happen on our main development branch (which also updated to v3.3.6 today). I have been unable to find the difference between both branches so far (they diverged a couple of months ago, but the base system is still regularly updated on both, and pretty similar). After some digging around, I assume this commit is related to our issue: https://github.com/ruby/ruby/commit/edeb0319f7a95dfe3f9b895bcf32371dd8514726 -- https://bugs.ruby-lang.org/