Note: the tests are still failing because the setup has atrophied without investment in keeping it up to date with newer XCode/OS X/iOS/tvOS/etc versions. This piece will require more follow up, but the test suite actually runs now, whereas it was not before with deprecated Mac images.
the previously configured version is no longer supported: https://circleci.com/docs/using-macos/
Note: the tests are still failing because the setup has atrophied without investment in keeping it up to date with newer XCode/OS X/iOS/tvOS/etc versions. This piece will require more follow up, but the test suite actually runs now, whereas it was not before with deprecated Mac images.