[ST-NNNN] Targeted Interoperability between Swift Testing and XCTest

[jerryjrchen]

Draft proposal for interop between Swift Testing and XCTest.

Preview it here: https://github.com/jerryjrchen/swift-evolution/blob/swt-xct-interop/proposals/testing/NNNN-targeted-interoperability-swift-testing-and-xctest.md

[grynspan]

Suggested change

	- Includes [exit testing][]
	- Includes `#expect(throws:)`
	- Includes [exit testing][]

Assuming #expect(throws:) will work! If it won't work, we need to call that out too.

[jerryjrchen]

Based on my understanding of that API, we're catching thrown errors and recording issues if not thrown. Since we'd need to add interop support for Swift Testing Issue as part of the default #expect, it seems to me the check throws variant should work too

[grynspan]

This environment variable affects the behaviour of XCTest API, right? Then I think we want to put it in the XCTEST_ namespace. 🤔

[grynspan]

Is this point about traits or about issue handling in general? (Since we're not translating traits.)

[jerryjrchen]

Well, we're not proposing that you could attach a Swift Testing trait to an XCTest test function. This is about the issue handling trait in a Swift Testing test, and what happens when it's asked to handle a XCTAssert failure.