StdlibUnittest: add a simple API for race tests

Author: gribozavr

stdlib/private/StdlibUnittest/RaceTest.swift

@@ -573,3 +573,31 @@ public func consumeCPU(units amountOfWork: Int) {
     }
   }
 }
+
+internal struct ClosureBasedRaceTest : RaceTestWithPerTrialData {
+  static var thread: () -> () = {}
+
+  class RaceData {}
+  typealias ThreadLocalData = Void
+  typealias Observation = Void
+
+  func makeRaceData() -> RaceData { return RaceData() }
+  func makeThreadLocalData() -> Void { return Void() }
+
+  func thread1(
+    _ raceData: RaceData, _ threadLocalData: inout ThreadLocalData
+  ) {
+    ClosureBasedRaceTest.thread()
+  }
+
+  func evaluateObservations(
+    _ observations: [Observation],
+    _ sink: (RaceTestObservationEvaluation) -> Void
+  ) {}
+}
+
+public func runRaceTest(trials: Int, threads: Int? = nil, body: () -> ()) {
+  ClosureBasedRaceTest.thread = body
+  runRaceTest(ClosureBasedRaceTest.self, trials: trials, threads: threads)
+}
+

validation-test/StdlibUnittest/RaceTest.swift

@@ -92,6 +92,16 @@ RaceTestSuite.test("fails") {
 // CHECK: stdout>>> Failure: 1 times
 // CHECK: stdout>>> Failure (65534): 3 times
 // CHECK: [     FAIL ] Race.fails
+
+RaceTestSuite.test("closure") {
+  let count = _stdlib_AtomicInt(0)
+  runRaceTest(trials: 10) {
+    _ = count.fetchAndAdd(1)
+  }
+  expectNotEqual(0, count.load())
+}
+// CHECK: [ RUN      ] Race.closure
+// CHECK: [       OK ] Race.closure
 // CHECK: Race: Some tests failed, aborting
 
 runAllTests()