After recently upgrading to macOS 10.15.6 (19G73) I got the following error trying to run tests on swift package, both from terminal and Xcode.
This copy of libswiftCore.dylib requires an OS version prior to 10.14.4. Exited with signal code 6
I'm running Xcode Version 11.6 (11E708) and Apple Swift version 5.2.4 (swiftlang-1220.127.116.11 clang-118.104.22.168), Target: x86_64-apple-darwin19.6.0.
The issue seems to affect both real projects and freshly created ones. Init and build run fine, test always give me the same error.
Running unit tests for an iOS project works without any issue.