test: add failing tests showing the issue in socketio#698

test/server.js

@@ -2759,13 +2759,23 @@ describe("server", () => {
         });
       });
 
-      it("should execute in multipart packet", (done) => {
+      it("should execute in multipart packet (websocket)", (done) => {
         const engine = listen((port) => {
-          const socket = new ClientSocket(`ws://localhost:${port}`);
+          const socket = new ClientSocket(`ws://localhost:${port}`, {
+            transports: ["websocket"],
+          });
           let i = 0;
           let j = 0;
 
           engine.on("connection", (conn) => {
+            conn.send("d", (transport) => {
+              i++;
+            });
+
+            conn.send("c", (transport) => {
+              i++;
+            });
+
             conn.send("b", (transport) => {
               i++;
             });

test/webtransport.mjs

@@ -373,6 +373,21 @@ describe("WebTransport", () => {
     });
   });
 
+  it("should invoke send callbacks (server to client)", (done) => {
+    setup({}, async ({ engine, h3Server, socket, reader }) => {
+      const messageCount = 4;
+      let receivedCallbacks = 0;
+
+      for (let i = 0; i < messageCount; i++) {
+        socket.send("hello", () => {
+          if (++receivedCallbacks === messageCount) {
+            success(engine, h3Server, done);
+          }
+        });
+      }
+    });
+  });
+
   it("should send some binary data (client to server)", (done) => {
     setup({}, async ({ engine, h3Server, socket, writer }) => {
       socket.on("data", (data) => {