test: add ListenConnections disconnect coverage

Author: xyzconstant

test/mp/test/listen_tests.cpp

@@ -289,6 +289,21 @@ KJ_TEST("ListenConnections accepts multiple connections")
     KJ_EXPECT(client3->client->add(3, 4) == 7);
 }
 
+KJ_TEST("ListenConnections survives a client that disconnects before being accepted")
+{
+    ListenSetup server;
+
+    // Connect and close before the server has a chance to accept() the
+    // connection.
+    int fd = server.listener.MakeConnectedSocket();
+    close(fd);
+
+    // The server should still accept and serve later clients.
+    auto client = std::make_unique<ClientSetup>(server.listener.MakeConnectedSocket());
+    server.WaitForConnectedCount(1);
+    KJ_EXPECT(client->client->add(1, 2) == 3);
+}
+
 } // namespace
 } // namespace test
 } // namespace mp