Add missing Linux APIs

Tests/Alchemy/_Utilities/Linux+Testing.swift

@@ -0,0 +1,33 @@
+#if os(Linux)
+extension XCTestCase {
+    /// Wait on an array of expectations for up to the specified timeout, and optionally specify whether they
+    /// must be fulfilled in the given order. May return early based on fulfillment of the waited on expectations.
+    ///
+    /// - Parameter expectations: The expectations to wait on.
+    /// - Parameter timeout: The maximum total time duration to wait on all expectations.
+    /// - Parameter enforceOrder: Specifies whether the expectations must be fulfilled in the order
+    ///   they are specified in the `expectations` Array. Default is false.
+    /// - Parameter file: The file name to use in the error message if
+    ///   expectations are not fulfilled before the given timeout. Default is the file
+    ///   containing the call to this method. It is rare to provide this
+    ///   parameter when calling this method.
+    /// - Parameter line: The line number to use in the error message if the
+    ///   expectations are not fulfilled before the given timeout. Default is the line
+    ///   number of the call to this method in the calling file. It is rare to
+    ///   provide this parameter when calling this method.
+    ///
+    /// - SeeAlso: XCTWaiter
+    @available(macOS 12.0, *)
+    func fulfillment(of expectations: [XCTestExpectation], timeout: TimeInterval, enforceOrder: Bool = false, file: StaticString = #file, line: Int = #line) async {
+        return await withCheckedContinuation { continuation in
+            // This function operates by blocking a background thread instead of one owned by libdispatch or by the
+            // Swift runtime (as used by Swift concurrency.) To ensure we use a thread owned by neither subsystem, use
+            // Foundation's Thread.detachNewThread(_:).
+            Thread.detachNewThread { [self] in
+                wait(for: expectations, timeout: timeout, enforceOrder: enforceOrder)
+                continuation.resume()
+            }
+        }
+    }
+}
+#endif