@Michael_Gottesman - sure! So, we were building XCTest using the CMake based build system, and then when it came time to test, we were using the old build.py script to build and run tests against. This means that we were doing a bunch of unnecessary work on the build bots but also that we would possibly package a version built completely differently from what we intended.
Really, I think this speaks to the complexity in the build script (impl) based orchestration. I'm hoping that we we can do an integrated build where we can test and build images all within a single system (CMake) to avoid this type of problem in the future.