Merge pull request #2744 from nikiforo/par-eval-v3

parEvalMap* - fix test "cancels unneeded"

Author: mpilquist

core/shared/src/test/scala/fs2/ParEvalMapSuite.scala

@@ -208,13 +208,15 @@ class ParEvalMapSuite extends Fs2Suite {
     }
 
     def check(pipe: Pipe[IO, IO[Unit], Unit]) =
-      IO.deferred[Unit]
-        .flatMap { d =>
-          val cancelled = IO.never.onCancel(d.complete(()).void)
-          val stream = Stream(u, cancelled).covary[IO]
+      (CountDownLatch[IO](2), IO.deferred[Unit])
+        .mapN { case (latch, d) =>
+          val w = latch.release *> latch.await
+          val cancelled = IO.uncancelable(poll => w *> poll(IO.never).onCancel(d.complete(()).void))
+          val stream = Stream(w *> u, cancelled).covary[IO]
           val action = stream.through(pipe).take(1).compile.drain
           action *> d.get
         }
+        .flatten
         .assertEquals(())
   }