After we’ve addressed all the deprecation warnings and successfully dual-booted an application, the next step in a Rails upgrade is often the most challenging: fixing the broken build.
At this point, the test suite is red, and our job is to bring it back to green. This phase can feel chaotic, but over the years at FastRuby.io, we’ve developed a process that makes it systematic and (relatively) predictable.
In this post, I’ll break down how we approach this step, what patterns we’ve noticed, and how we debug the trickiest failures.
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