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[ST-NNNN] Targeted Interoperability between Swift Testing and XCTest #2982

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[ST-NNNN] Targeted Interoperability between Swift Testing and XCTest #2982

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@jerryjrchen jerryjrchen commented Oct 2, 2025 •
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stmontgomery
stmontgomery reviewed Oct 2, 2025
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proposals/testing/NNNN-targeted-interoperability-swift-testing-and-xctest.md Outdated
empowered to choose Swift Testing when writing new tests or test helpers, as
it will work properly in both types of tests.

We don't propose supporting interoperability for APIs without risk of data loss,
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We don't propose supporting interoperability for APIs without risk of data loss,
We don't propose supporting interoperability for APIs which are not lossy without interop,

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Don't not hate the double negative here, but can't think of better wording at the moment :)

@grynspan grynspan changed the title Targeted Interoperability between Swift Testing and XCTest [ST-NNNN] Targeted Interoperability between Swift Testing and XCTest Oct 3, 2025
@grynspan grynspan added the TWG Contains topics under the domain of the Testing Workgroup label Oct 3, 2025
grynspan
grynspan reviewed Oct 3, 2025
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proposals/testing/NNNN-targeted-interoperability-swift-testing-and-xctest.md
from XCTest to Swift Testing. For issue details unique to XCTest, we will
include them as a comment when constructing the Swift Testing issue.

Note that no changes are proposed for the `XCTSkip` API, because they already
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Can we think of other XCTest features that are explicitly not supported and should be called out here?

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XCTestAssertion and XCTWaiter, I guess!

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(I assume you meant XCTestExpectation)

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I'm so tired…

grynspan
grynspan reviewed Oct 3, 2025
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proposals/testing/NNNN-targeted-interoperability-swift-testing-and-xctest.md
We propose supporting the following Swift Testing APIs in XCTest:

- `#expect` and `#require`
- Includes [exit testing][]
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- 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.

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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
grynspan reviewed Oct 3, 2025
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proposals/testing/NNNN-targeted-interoperability-swift-testing-and-xctest.md
usage occurs when running Swift Testing tests by turning those warnings into a
`fatalError`.

Configure the interoperability mode when running tests using the
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This environment variable affects the behaviour of XCTest API, right? Then I think we want to put it in the XCTEST_ namespace. 🤔

@jerryjrchen jerryjrchen force-pushed the swt-xct-interop branch 3 times, most recently from ff379e8 to 0545e6c Compare October 3, 2025 18:16
grynspan
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proposals/testing/NNNN-targeted-interoperability-swift-testing-and-xctest.md
- [Expected failures][], such as `XCTExpectFailure`: marking a Swift Testing
issue in this way will generate a runtime warning issue.
- [`XCTAttachment`][XCTest attachments]
- [Issue handling traits][]: we will make our best effort to translate issues
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Is this point about traits or about issue handling in general? (Since we're not translating traits.)

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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.

@stmontgomery stmontgomery added workgroup: needs implementation This proposal needs more implementation work before it can be reviewed workgroup: needs pitch This proposal needs to spend more time in pitch before it can be reviewed labels Oct 3, 2025
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