diff --git a/test/namespaces.ts b/test/namespaces.ts
index d78d25f86d..ffe9602c30 100644
--- a/test/namespaces.ts
+++ b/test/namespaces.ts
@@ -6,6 +6,7 @@ import {
   createClient,
   successFn,
   createPartialDone,
+  assert,
 } from "./support/util";
 
 describe("namespaces", () => {
@@ -417,6 +418,7 @@ describe("namespaces", () => {
     socket1.on("a", successFn(done, io, socket1, socket2));
 
     socket2.on("connect", () => {
+      assert(socket2.id);
       io.except(socket2.id).emit("a");
     });
   });
@@ -435,6 +437,7 @@ describe("namespaces", () => {
     socket1.on("a", successFn(done, io, socket1, socket2));
 
     socket2.on("connect", () => {
+      assert(socket2.id);
       nsp.except(socket2.id).emit("a");
     });
   });
diff --git a/test/support/util.ts b/test/support/util.ts
index ac78016fbe..1742010f48 100644
--- a/test/support/util.ts
+++ b/test/support/util.ts
@@ -63,6 +63,16 @@ export function successFn(
   return () => success(done, sio, ...clientSockets);
 }
 
+/**
+ * Asserts a condition so that typescript will recognize the assertion!
+ *
+ * Uses expect's `ok` check on condition
+ * @param condition
+ */
+export function assert(condition: any): asserts condition {
+  expect(condition).to.be.ok();
+}
+
 export function getPort(io: Server): number {
   // @ts-ignore
   return io.httpServer.address().port;
diff --git a/test/uws.ts b/test/uws.ts
index 13ede296af..3a287e6468 100644
--- a/test/uws.ts
+++ b/test/uws.ts
@@ -7,6 +7,7 @@ import { Server } from "..";
 import { io as ioc, Socket as ClientSocket } from "socket.io-client";
 import request from "supertest";
 import expect from "expect.js";
+import { assert } from "./support/util";
 
 const createPartialDone = (done: (err?: Error) => void, count: number) => {
   let i = 0;
@@ -134,6 +135,8 @@ describe("socket.io with uWebSocket.js-based engine", () => {
     clientWSOnly.on("hello", partialDone);
     clientPollingOnly.on("hello", partialDone);
     clientCustomNamespace.on("hello", shouldNotHappen(done));
+    assert(clientWSOnly.id);
+    assert(clientPollingOnly.id);
 
     io.of("/").sockets.get(clientWSOnly.id)!.join("room1");
     io.of("/").sockets.get(clientPollingOnly.id)!.join("room1");
@@ -148,6 +151,8 @@ describe("socket.io with uWebSocket.js-based engine", () => {
     clientWSOnly.on("hello", partialDone);
     clientPollingOnly.on("hello", partialDone);
     clientCustomNamespace.on("hello", shouldNotHappen(done));
+    assert(clientWSOnly.id);
+    assert(clientPollingOnly.id);
 
     io.of("/").sockets.get(clientWSOnly.id)!.join("room1");
     io.of("/").sockets.get(clientPollingOnly.id)!.join("room2");
@@ -163,6 +168,8 @@ describe("socket.io with uWebSocket.js-based engine", () => {
     clientPollingOnly.on("hello", shouldNotHappen(done));
     clientCustomNamespace.on("hello", shouldNotHappen(done));
 
+    assert(clientWSOnly.id);
+    assert(clientPollingOnly.id);
     io.of("/").sockets.get(clientWSOnly.id)!.join("room1");
     io.of("/").sockets.get(clientPollingOnly.id)!.join("room2");
 
@@ -177,6 +184,9 @@ describe("socket.io with uWebSocket.js-based engine", () => {
     clientPollingOnly.on("hello", partialDone);
     clientCustomNamespace.on("hello", shouldNotHappen(done));
 
+    assert(client.id);
+    assert(clientWSOnly.id);
+    assert(clientPollingOnly.id);
     io.of("/").sockets.get(client.id)!.join("room1");
     io.of("/").sockets.get(clientPollingOnly.id)!.join("room1");
 
@@ -189,6 +199,7 @@ describe("socket.io with uWebSocket.js-based engine", () => {
   it("should not crash when socket is disconnected before the upgrade", (done) => {
     client.on("disconnect", () => done());
 
+    assert(client.id);
     io.of("/").sockets.get(client.id)!.disconnect();
   });