I recently discovered that unit tests and UI tests for a macOS Xcode project will fail with obscure error messages if the hardened runtime is enabled. It took me awhile to realize what the actual source of the problem was, because the error messages led me in the wrong direction. Hopefully this will save you some time.
I have started using GitHub Actions for CI on a new project as a replacement for my usual setup on Travis CI. It generally seems to be much faster and more reliable so far. It also has an equivalent feature set, as far as I can tell. But one issue that I have run into is selecting a specific Xcode version, which is a bit cumbersome and not fully documented.