[SR-15561] XCTestCase crashes due to use of expectations in async/await method on Linux

[tonyarnold]

Previous ID	SR-15561
Radar	rdar://85344643
Original Reporter	@tonyarnold
Type	Bug
Status	Resolved
Resolution	Done

Environment

I was using the swiftlang/swift:nightly-5.5-focal Docker tag on the 1st December, 2021.

Additional Detail from JIRA

Votes	0
Component/s	XCTest
Labels	Bug
Assignee	@stmontgomery
Priority	Medium

md5: 219c66c7d78a9418491933d5732beff1

Issue Description:

It appears that XCTestCase.expectation(description: "…") calls through to XCTestCase.addExpectation(…) which asserts that it is being called from the main thread. See https://github.com/apple/swift-corelibs-xctest/blob/1b0e65c2a3453636b5b9bdf24111285426187cca/Sources/XCTest/Public/XCTestCase.swift#L63 for the implementation of this.

When running in an async test case, the test case is not always run on the main thread, so the test fails and crashes the running suite due to this assertion.

A simple test case is to call the following code within an async test, something like:

class MyTests: XCTestCase {
    func testAThing() async throws {
        let expectation = expectation(description: "Sending email")
    }
}

And then run it on Linux using any recent Swift 5.5 snapshot.

The same code runs fine under macOS under Xcode 13.2 beta 2, so this appears to be a difference between Swift's implementation of XCTest and Xcode's.

[stmontgomery]

This is because the XCTestCase methods which create and return XCTestExpectations currently require calling on the main thread:

https://github.com/apple/swift-corelibs-xctest/blob/1b0e65c2a3453636b5b9bdf24111285426187cca/Sources/XCTest/Public/XCTestCase.swift#L63

But we should relax those constraints for the Corelibs implementation of XCTest since that's something we recently did in the Xcode implementation

[stmontgomery]

Sorry, I overlooked Tony's comment which says the same thing! Sounds like we're on the same page 🙂

[stmontgomery]

#340

[stmontgomery]

56501e7

[tonyarnold]

Fantastic, thanks @stmontgomery! 😃