Fix flaky test TransactionTests.testCancelAsyncRequest (#707)

* Fix flaky test `TransactionTests.testCancelAsyncRequest`

Resolves #706.
The continuation is resumed with the cancelation error before we cancel the scheduled request.
https://github.com/swift-server/async-http-client/blob/62c06d47c8d21c91335e9f8998589e4ce31411e6/Sources/AsyncHTTPClient/AsyncAwait/Transaction.swift#L290C10-L294

Therefore this test is inherently flaky. The fix waits up to one second for the scheduled request to be canceled.

* self.fulfillment(of:) is not available on Linux

* Fix formatting

* Fix 5.6

Author: dnadoba

Tests/AsyncHTTPClientTests/RequestBagTests.swift

@@ -961,13 +961,18 @@ class UploadCountingDelegate: HTTPClientResponseDelegate {
     }
 }
 
-class MockTaskQueuer: HTTPRequestScheduler {
+final class MockTaskQueuer: HTTPRequestScheduler {
     private(set) var hitCancelCount = 0
 
-    init() {}
+    let onCancelRequest: (@Sendable (HTTPSchedulableRequest) -> Void)?
 
-    func cancelRequest(_: HTTPSchedulableRequest) {
+    init(onCancelRequest: (@Sendable (HTTPSchedulableRequest) -> Void)? = nil) {
+        self.onCancelRequest = onCancelRequest
+    }
+
+    func cancelRequest(_ request: HTTPSchedulableRequest) {
         self.hitCancelCount += 1
+        self.onCancelRequest?(request)
     }
 }
 

Tests/AsyncHTTPClientTests/TransactionTests.swift

@@ -27,6 +27,9 @@ typealias PreparedRequest = HTTPClientRequest.Prepared
 final class TransactionTests: XCTestCase {
     func testCancelAsyncRequest() {
         guard #available(macOS 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0, *) else { return }
+        // creating the `XCTestExpectation` off the main thread crashes on Linux with Swift 5.6
+        // therefore we create it here as a workaround which works fine
+        let scheduledRequestCanceled = self.expectation(description: "scheduled request canceled")
         XCTAsyncTest {
             let embeddedEventLoop = EmbeddedEventLoop()
             defer { XCTAssertNoThrow(try embeddedEventLoop.syncShutdownGracefully()) }
@@ -43,19 +46,25 @@ final class TransactionTests: XCTestCase {
                 preferredEventLoop: embeddedEventLoop
             )
 
-            let queuer = MockTaskQueuer()
+            let queuer = MockTaskQueuer { _ in
+                scheduledRequestCanceled.fulfill()
+            }
             transaction.requestWasQueued(queuer)
 
+            XCTAssertEqual(queuer.hitCancelCount, 0)
             Task.detached {
                 try await Task.sleep(nanoseconds: 5 * 1000 * 1000)
                 transaction.cancel()
             }
 
-            XCTAssertEqual(queuer.hitCancelCount, 0)
             await XCTAssertThrowsError(try await responseTask.value) { error in
                 XCTAssertTrue(error is CancellationError, "unexpected error \(error)")
             }
-            XCTAssertEqual(queuer.hitCancelCount, 1)
+
+            // self.fulfillment(of:) is not available on Linux
+            _ = {
+                self.wait(for: [scheduledRequestCanceled], timeout: 1)
+            }()
         }
     }