Enable swift-testing by default.

[grynspan]

This PR sets the default state of --{enable,disable}-experimental-swift-testing to enabled.

This PR is speculative.

[grynspan]

@swift-ci please test

[grynspan]

@swift-ci please test

[grynspan]

@swift-ci please test

[Jerry-Carter]

Hoping to see this change made soon. Some general comments, mostly related to this issue.

The current behavior is rather unintuitive. WWDC24 suggests that Swift Testing is now the preferred test framework, but these tests aren't actually executed unless the command line argument --enable-swift-testing is given. The XCTest cases are always executed. When only Swift Testing is used, the build processes ends with 'Executed 0 tests, with 0 failures (0 unexpected) in 0.000 (0.001) seconds' which is confusing and false. At a minimum, may I suggest changing

Test run started  → Swift Test execution started
Test Suite 'All tests'  → XCTest Suite 'All tests'
Executed 0 tests, with 0 failures  → XCTest complete.  Executed 0 tests, with 0 failures

so that the stages are a bit clearer.

I understand from the forum discussion that the code is compiled, then the Swift Testing cases are executed (if the flag is specified), and then the XCTest cases are executed with the 'Executed 0 tests' message originating from the later. However, it appears that plugins are re-executed between the Swift Testing and XCTest stages which (1) feels unnecessary and (2) breaks up the results from unit testing.

Finally, I appreciate that the unit tests are being performed in parallel but I wish the output from Suites was grouped somehow rather than interwoven. In my mind, Suites represent the fundamental conceptual units with the underlaying Test functions being supporting details. I'd love to see something like

▢ Test run started.
↳ Testing Library Version: 75.9 (arm64e-apple-macos13.0)
▢ Suite "LongTests" started
      ▢ Test dataDiscombobulation() started.
      ☑️ Test reskewingWidgets() passed after 52.182 seconds.
 ☑️ Suite "ShortTests" passed after 0.390 seconds.
      ☑️ Test checkName() passed after 0.02 seconds.
      ☑️ Test sortOrder() passed after 0.389 seconds.

at runtime, but would also welcome an option to generate a final test report.

[grynspan]

Thank you for your feedback, @Jerry-Carter. The current behaviour on macOS (where you need to specify the flag) is a known issue with Xcode 16's built-in Swift toolchain. We are working to resolve it.

[grynspan]

Superseded by #7766.