I've had a lot of success bringing C++ dependencies under SPM management. It's created a package based import mechanism without storing binaries anywhere, and it's a quick and easy process for smaller dependencies.
But the tests are one thing I haven't been able to bring with me to SPM. GTest is the defecto testing framework for C++, and I haven't seen a way to invoke it from a test target. And until C++ compatibility lands in Swift, there's no way to exercise the C++ (easily) from XCTest.
I also poked around and it looks like there were some stories about third party test framework support many years ago, and these were closed.
Am I correct in thinking there is no clear way to test C++, in a cross platform way, from SPM? And no way to integrate GTest?