Open Radar

 
Summary:
Realm’s Objective-C/Swift tests run fine with Xcode 9 beta 4 in Swift 3 mode, but the Swift tests don’t run in Swift 4 mode.

Steps to Reproduce:
1. Open Realm.xcodeproj in Xcode 9 beta 4 from the attached archive
2. Select the “Realm” scheme
3. Run unit tests (cmd-U)
4. Observe that the unit tests from Swift sources do not run
5. Perform a `git reset —hard` command to revert the `SWIFT_VERSION` configuration setting to 3.0
6. Run unit tests again (cmd-U)
7. Observe that the unit tests from Swift sources now run

Expected Results:
For Swift unit test sources that compile and run in `SWIFT_VERSION=3.0` mode, they should also compile and run in `SWIFT_VERSION=4.0` mode, or in the case of a compilation error, should display that compilation error and abort the test process.

Actual Results:
Changing the SWIFT_VERSION mode from 3.0 to 4.0 just skips the Swift sources, neither compiling them nor running their unit tests.

Version:
Xcode 9 beta 4 (9M189t)

Notes:
Interestingly enough, Xcode’s test navigator pane does _detect_ the tests, but doesn’t compile them or run them.

I’ve attached a video walking through the reproduction steps as well as an archive of the project.