fix: more reliable wait_pids in test

riot/runtime/import.ml

@@ -211,10 +211,12 @@ let wait_pids pids =
   (* And we can enter the receive loop, filtering out the pids as they come.
      When the list of pids becomes empty, we exit the recursion. *)
   let rec do_wait pids =
-    match receive ~selector () with
-    | Process_down pid ->
-        let pids = List.filter (fun pid' -> not (Pid.equal pid' pid)) pids in
-        if List.length pids = 0 then () else do_wait pids
+    if List.length pids = 0 then ()
+    else
+      match receive ~selector () with
+      | Process_down pid ->
+          let pids = List.filter (fun pid' -> not (Pid.equal pid' pid)) pids in
+          do_wait pids
   in
   do_wait pids
 

test/link_processes_test.ml

@@ -26,11 +26,12 @@ let main () =
         loop ())
   in
 
-  List.iter monitor [ pid1; pid2 ];
-
-  sleep 0.5;
-  (* once we send this exit signal to pid1, and it dies, it should take pid2 down with it *)
-  exit pid1 Normal;
+  let _ =
+    spawn (fun () ->
+        sleep 0.5;
+        (* once we send this exit signal to pid1, and it dies, it should take pid2 down with it *)
+        exit pid1 Normal)
+  in
 
   (* so we'll wait for both pids to be dead *)
   wait_pids [ pid1; pid2 ];