TestChannel.send never fails, even after the channel has been shut down #4222

package example.testing

import zio._
import zio.http._
import zio.http.ChannelEvent.Read
import zio.test._

// Repro: TestChannel.send never fails, even after the channel has been shut down.
// On a real (Netty) connection, sending after the peer disconnects fails the Task
// (e.g. ClosedChannelException). TestChannel.send just does `out.offer(in).unit`,
// which is backed by Queue#offer : UIO[Boolean] and can never fail.
object TestChannelSendAfterShutdownRepro extends ZIOSpecDefault {
  def spec = test("channel.send fails after shutdown on a real channel, but not on TestChannel") {
    for {
      resultPromise <- Promise.make[Nothing, Either[Throwable, Unit]]
      server = Handler.webSocket[Any] { channel =>
        for {
          _      <- channel.receive // handshake complete event
          _      <- channel.shutdown // simulate the peer/connection going away
          result <- channel.send(Read(WebSocketFrame.text("should fail: channel is closed"))).either
          _      <- resultPromise.succeed(result)
        } yield ()
      }
      _        <- TestClient.installSocketApp(server)
      _        <- ZIO.serviceWithZIO[Client](_.socket(Handler.webSocket[Any](_ => ZIO.unit)))
      result   <- resultPromise.await
    } yield assertTrue(result.isLeft) // FAILS today: result is Right(()) — send after shutdown should have failed
  }.provide(TestClient.layer, Scope.default)
}

case class TestChannel(
  in: Queue[WebSocketChannelEvent],
  out: Queue[WebSocketChannelEvent],
  promise: Promise[Nothing, Unit],
) extends WebSocketChannel {
  ...
  def send(in: WebSocketChannelEvent)(implicit trace: Trace): Task[Unit] =
    out.offer(in).unit
  ...
  def shutdown(implicit trace: Trace): UIO[Unit] =
    in.offer(ChannelEvent.Unregistered) *>
      out.offer(ChannelEvent.Unregistered) *>
      promise.succeed(()).unit
}