StoreKitConfigTestCase: improved waitForStoreKitTestIfNeeded

I did this in hopes that it would work around `FB11799675`, but alas it didn't. I still think it's a useful refactor.

- Combined `hasWaited` and `waitLock` into a single `Atomic`
- Replaced `Thread.sleep` with `Task.sleep` to avoid blocking the thread. This way if `StoreKitTestSession` needs to do anything on the main thread, it can since it's no longer blocked.
- Moved call to `waitForStoreKitTestIfNeeded` _before_ finishing transactions. I did this in hopes that by the time we call that method, these transactions are gone.

Sources/Misc/Concurrency/Atomic.swift

@@ -35,6 +35,9 @@ import Foundation
  *     $0.bar = 2
  *     $0.x = "new X"
  * }
+ *
+ * // write value and get previous value
+ * let oldValue = foo.getAndSet(newValue)
  * ```
  *
  * Or for single-line read/writes:
@@ -65,6 +68,14 @@ internal final class Atomic<T> {
         }
     }
 
+    @discardableResult
+    func getAndSet(_ newValue: T) -> T {
+        return self.modify { currentValue in
+            defer { currentValue = newValue }
+            return currentValue
+        }
+    }
+
     @discardableResult
     func withValue<Result>(_ action: (T) throws -> Result) rethrows -> Result {
         return try lock.perform {

Tests/StoreKitUnitTests/StoreKitConfigTestCase.swift

@@ -26,11 +26,10 @@ class StoreKitConfigTestCase: TestCase {
         return .seconds(Int(Self.requestTimeout))
     }
 
-    private static var hasWaited = false
-    private static let waitLock = Lock()
-    private static let waitTimeInSeconds: Double? = {
+    private static let hasWaited: Atomic<Bool> = false
+    private static let waitTimeInSeconds: TimeInterval? = {
         ProcessInfo.processInfo.environment["CIRCLECI_STOREKIT_TESTS_DELAY_SECONDS"]
-            .flatMap(Double.init)
+            .flatMap(TimeInterval.init)
     }()
 
     var testSession: SKTestSession!
@@ -47,12 +46,12 @@ class StoreKitConfigTestCase: TestCase {
         self.testSession.disableDialogs = true
         self.testSession.clearTransactions()
 
+        await self.waitForStoreKitTestIfNeeded()
+
         if #available(iOS 15.0, tvOS 15.0, macOS 12.0, watchOS 8.0, *) {
             await self.finishAllUnfinishedTransactions()
         }
 
-        self.waitForStoreKitTestIfNeeded()
-
         let suiteName = "StoreKitConfigTests"
         self.userDefaults = UserDefaults(suiteName: suiteName)
         self.userDefaults.removePersistentDomain(forName: suiteName)
@@ -89,21 +88,16 @@ class StoreKitConfigTestCase: TestCase {
 @available(iOS 14.0, tvOS 14.0, macOS 11.0, watchOS 7.0, *)
 private extension StoreKitConfigTestCase {
 
-    func waitForStoreKitTestIfNeeded() {
+    func waitForStoreKitTestIfNeeded() async {
         // StoreKitTest seems to take a few seconds to initialize, and running tests before that
         // might result in failure. So we give it a few seconds to load before testing.
 
         guard let waitTime = Self.waitTimeInSeconds else { return }
+        guard !Self.hasWaited.getAndSet(true) else { return }
 
-        Self.waitLock.perform {
-            if !Self.hasWaited {
-                Logger.warn("Delaying tests for \(waitTime) seconds for StoreKit initialization...")
-
-                Thread.sleep(forTimeInterval: waitTime)
+        Logger.warn("Delaying tests for \(waitTime) seconds for StoreKit initialization...")
 
-                Self.hasWaited = true
-            }
-        }
+        try? await Task.sleep(nanoseconds: DispatchTimeInterval(waitTime).nanoseconds)
     }
 
     func clearReceiptIfExists() {

Tests/UnitTests/Misc/AtomicTests.swift

@@ -39,6 +39,14 @@ class AtomicTests: TestCase {
         expect(result) == false
     }
 
+    func testGetAndSet() {
+        let atomic = Atomic(false)
+        let oldValue = atomic.getAndSet(true)
+
+        expect(oldValue) == false
+        expect(atomic.value) == true
+    }
+
     func testWithValue() {
         let atomic = Atomic(10)
         let result: Int = atomic.withValue { $0 + 10 }