test: regression test for bug

test/dune

@@ -1,6 +1,7 @@
 (tests
  (names
   t_fib
+  t_ws_pool_confusion
   t_bench1
   t_fib_rec
   t_futs1

test/t_ws_pool_confusion.ml

@@ -0,0 +1,28 @@
+open Moonpool
+
+let delay () = Thread.delay 0.001
+
+let run ~p_main:_ ~p_sub () =
+  let f1 =
+    Fut.spawn ~on:p_sub (fun () ->
+        delay ();
+        1)
+  in
+  let f2 =
+    Fut.spawn ~on:p_sub (fun () ->
+        delay ();
+        2)
+  in
+  Fut.wait_block_exn f1 + Fut.wait_block_exn f2
+
+let () =
+  let p_main = Ws_pool.create ~num_threads:2 () in
+  let p_sub = Ws_pool.create ~num_threads:10 () in
+
+  let futs = List.init 8 (fun _ -> Fut.spawn ~on:p_main (run ~p_main ~p_sub)) in
+
+  let l = List.map Fut.wait_block_exn futs in
+  assert (l = List.init 8 (fun _ -> 3));
+
+  print_endline "ok";
+  ()