Port SwiftPMBuildSystemTests to Swift Testing

Author: owenv

Sources/SKTestSupport/Expectations.swift

@@ -0,0 +1,27 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+public import Testing
+
+public func expectThrowsError<T>(
+  _ expression: @autoclosure () async throws -> T,
+  _ message: @autoclosure () -> String = "",
+  sourceLocation: SourceLocation = #_sourceLocation,
+  errorHandler: (_ error: Error) -> Void = { _ in }
+) async {
+  do {
+    _ = try await expression()
+    Issue.record("Expression was expected to throw but did not throw", sourceLocation: sourceLocation)
+  } catch {
+    errorHandler(error)
+  }
+}