For anyone needing this now, and can't wait for a new version of Xcode, this linker path seems to work: swift test --configuration debug -Xlinker -rpath -Xlinker "$(xcode-select -p)/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift-5.5/macosx"
Note that you may need to add the -Xlinker -rpath -Xlinker "$(xcode-select -p)/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift-5.5/macosx" bit to your swift build commands as well, as the tests may run without re-building in some circumstances.