Unable to use RunLoop to allow task to advance

[jonreid]

Description

Say we have a UIKit table view controller which loads its data by doing this inside viewDidLoad():

Task {
    results = await viewModel.load()
    self.tableView.reloadData()
}

I am able to test this in XCTest by pumping the run loop. This does not work in Swift Testing.

Expected behavior

With XCTest, I can allow the task to proceed by polling for the expected results in a loop that calls:

RunLoop.current.run(until: Date(timeIntervalSinceNow: 0.01))

Actual behavior

With Swift Testing, pumping the run loop does not advance the task.

I added print statements in 2 places: one inside the Task after the await, and another at the end of the test case, both XCTest and Swift Testing.

• XCTest: Task completes, then test completes
• Swift Testing: Test completes, then task completes

Steps to reproduce

In https://github.com/jonreid/ExpectToEventuallyEqual there is a SampleApp that contains both XCTest and Swift Testing targets. The print statements are in place inside TableViewController viewDidLoad(), and at the end of test_numberOfRows and numberOfRows. Run each to see the difference in behavior.

swift-testing version/commit hash

Xcode 16.0.0 built-in

Swift & OS version (output of swift --version ; uname -a)

swift-driver version: 1.115 Apple Swift version 6.0 (swiftlang-6.0.0.9.10 clang-1600.0.26.2) Target: arm64-apple-macosx14.0 Darwin Llama.local 23.6.0 Darwin Kernel Version 23.6.0: Mon Jul 29 21:14:30 PDT 2024; root:xnu-10063.141.2~1/RELEASE_ARM64_T6000 arm64

[grynspan]

Just to clarify: is the test in question marked @MainActor? Is it async?

[jonreid]

It is @MainActor. Tried both with and without async.

[grynspan]

Alright, thanks. Interactions between the main actor and main run loop are controlled by the Swift runtime, so I'm going to move this issue to the main Swift repo.