TaskLocal test trait

Sources/Testing/CMakeLists.txt

@@ -130,6 +130,7 @@ add_library(Testing
   Traits/Tags/Tag+Macro.swift
   Traits/Tags/Tag+Predefined.swift
   Traits/TimeLimitTrait.swift
+  Traits/TaskLocalTrait.swift
   Traits/Trait.swift)
 target_link_libraries(Testing PRIVATE
   _TestDiscovery

Sources/Testing/Traits/TaskLocalTrait.swift

@@ -0,0 +1,57 @@
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2026 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 Swift project authors
+//
+
+extension Trait {
+  /// Constructs a trait that binds a task local value for the duration of a test
+  /// or suite.
+  ///
+  /// - Parameters:
+  ///   - taskLocal: The task local to bind the value to.
+  ///   - value: The value to set.
+  ///
+  /// ```swift
+  /// @Suite(.taskLocal($myValue, 42))
+  /// struct MyTests {
+  ///   // ...
+  /// }
+  /// ```
+  ///
+  /// - Note: You must define the task local outside the test target where the trait is used.
+  public static func taskLocal<Value: Sendable>(
+    _ taskLocal: TaskLocal<Value>,
+    _ value: @autoclosure @escaping @Sendable () throws -> Value
+  ) -> Self
+  where Self == TaskLocalTrait<Value> {
+    TaskLocalTrait(taskLocal: taskLocal, value: value)
+  }
+}
+
+/// A type that that binds a task local value for the duration of a test or suite.
+///
+/// To add this trait to a test, use ``Trait/taskLocal(_:_:)``.
+public struct TaskLocalTrait<Value: Sendable>: SuiteTrait, TestTrait, TestScoping {
+  /// This trait's task local.
+  fileprivate var taskLocal: TaskLocal<Value>
+
+  /// This trait's value.
+  fileprivate var value: @Sendable () throws -> Value
+
+  public func provideScope(
+    for test: Test,
+    testCase: Test.Case?,
+    performing function: @concurrent () async throws -> Void
+  ) async throws {
+    try await taskLocal.withValue(value(), operation: function)
+  }
+}
+
+#if DEBUG
+  @TaskLocal var dummyLocal = false
+#endif

Tests/TestingTests/Traits/TaskLocalTraitTests.swift

@@ -0,0 +1,22 @@
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2026 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 Swift project authors
+//
+
+@testable @_spi(Experimental) @_spi(ForToolsIntegrationOnly) import Testing
+
+@Suite("Task Local Tests", .tags(.traitRelated))
+struct TaskLocalTests {
+  @Test(
+    ".taskLocal trait",
+    .taskLocal($dummyLocal, true)
+  )
+  func taskLocalBinding() throws {
+    #expect(dummyLocal == true)
+  }
+}