…r so don't have access to testdatas, etc.

To get C++17 support, Xcode 9.3+ is needed, requiring
at least macOS 10.13 on the build machine. To use C++17
library features and link against the C++ runtime library,
set MACOSX_DEPLOYMENT_TARGET to "10.13" or "10.14"
(or higher) - macOS 10.13 offers partial C++17 support
(e.g., the filesystem header is in experimental,
offering #include <experimental/filesystem> instead
of #include <filesystem>); macOS 10.14 has full C++17
support.
"""

…which should be good enough?