Make SwiftPM run XCTest and Testing tests in parallel by default?

[vanvoorden (Rick van Voorden)]

@smontgomery

I think that energy would be better spent encouraging usages of XCTest to transition to Swift Testing, and fixing any parallelization blockers that are encountered along the way.

The last place I am blocked is one of my open source macro packages… we support the 5.10 toolchain and we also support swift-syntax 510.

It looks like there is more support for Swift Testing macros from the 600 release… but that would then lead to "two tests" if I still want to support the 510 release.

Swift-Testing Support for Macros?

The swift-syntax 600.0.0 prereleases contain a SwiftSyntaxMacrosGenericTestSupport modules that can be used to test macros using swift-testing. Copying from the swift-syntax pending 600.0.0 release notes SwiftSyntaxMacrosGenericTestSupport A version of the SwiftSyntaxMacrosTestSupport module that doesn't depend on Foundation or XCTest and can thus be used to write macro tests using swift-testing . Since swift-syntax can't depend on swift-testing (which would incur a circular dependency sinc…