diff --git a/test/unit/ut_cpp20coro_ep.cpp b/test/unit/ut_cpp20coro_ep.cpp
index a0dd79493..50735e115 100644
--- a/test/unit/ut_cpp20coro_ep.cpp
+++ b/test/unit/ut_cpp20coro_ep.cpp
@@ -33,6 +33,7 @@ BOOST_AUTO_TEST_CASE(pingresp_tout_v311) {
                 version,
                 ioc.get_executor()
             );
+            ep->set_pingresp_recv_timeout_ms(0); // for coverage
             ep->set_pingresp_recv_timeout_ms(10);
             // prepare connect
             {
diff --git a/test/unit/ut_ep_pid.cpp b/test/unit/ut_ep_pid.cpp
index 4d8140682..bc7a8669b 100644
--- a/test/unit/ut_ep_pid.cpp
+++ b/test/unit/ut_ep_pid.cpp
@@ -44,6 +44,16 @@ BOOST_AUTO_TEST_CASE(wait_until) {
         ep->acquire_unique_packet_id_wait_until(as::use_future).get();
     }
 
+    as::dispatch(
+        as::bind_executor(
+            ep->strand(),
+            [&] {
+                auto pid_opt = ep->acquire_unique_packet_id();
+                BOOST_CHECK(!pid_opt);
+            }
+        )
+    );
+
     auto fut1 = ep->acquire_unique_packet_id_wait_until(as::use_future);
     auto fut2 = ep->acquire_unique_packet_id_wait_until(as::use_future);
     auto fut3 = ep->acquire_unique_packet_id_wait_until(as::use_future);
diff --git a/test/unit/ut_ep_size_max.cpp b/test/unit/ut_ep_size_max.cpp
index 829fd8e08..9132f4eee 100644
--- a/test/unit/ut_ep_size_max.cpp
+++ b/test/unit/ut_ep_size_max.cpp
@@ -139,6 +139,121 @@ BOOST_AUTO_TEST_CASE(client_send) {
     th.join();
 }
 
+BOOST_AUTO_TEST_CASE(client_send_no_store) {
+    auto version = am::protocol_version::v5;
+    as::io_context ioc;
+    auto guard = as::make_work_guard(ioc.get_executor());
+    std::thread th {
+        [&] {
+            ioc.run();
+        }
+    };
+
+    auto ep = am::endpoint<async_mqtt::role::client, async_mqtt::stub_socket>::create(
+        version,
+        // for stub_socket args
+        version,
+        ioc
+    );
+
+    ep->next_layer().set_close_checker(
+        [&] { BOOST_TEST(false); }
+    );
+
+    auto connect = am::v5::connect_packet{
+        true,   // clean_start
+        0x1234, // keep_alive
+        am::allocate_buffer("cid1"),
+        am::nullopt, // will
+        am::allocate_buffer("user1"),
+        am::allocate_buffer("pass1")
+    };
+
+    auto connack = am::v5::connack_packet{
+        false,   // session_present
+        am::connect_reason_code::success,
+        am::properties{
+            am::property::maximum_packet_size{21}
+        }
+    };
+
+    ep->next_layer().set_recv_packets(
+        {
+            // receive packets
+            connack,
+        }
+    );
+
+    // send connect
+    ep->next_layer().set_write_packet_checker(
+        [&](am::packet_variant wp) {
+            BOOST_TEST(connect == wp);
+        }
+    );
+    {
+        auto ec = ep->send(connect, as::use_future).get();
+        BOOST_TEST(!ec);
+    }
+
+    // recv connack
+    {
+        auto pv = ep->recv(as::use_future).get();
+        BOOST_TEST(connack == pv);
+    }
+
+    // size: 21bytes
+    auto pid_opt1 = ep->acquire_unique_packet_id(as::use_future).get();
+    BOOST_TEST(pid_opt1.has_value());
+    auto publish_1_q1 = am::v5::publish_packet(
+        *pid_opt1,
+        am::allocate_buffer("topic1"),
+        am::allocate_buffer("payload1"),
+        am::qos::at_least_once,
+        am::properties{}
+    );
+
+    // size: 22bytes
+    auto pid_opt2 = ep->acquire_unique_packet_id(as::use_future).get();
+    BOOST_TEST(pid_opt2.has_value());
+    auto publish_2_q1 = am::v5::publish_packet(
+        *pid_opt2,
+        am::allocate_buffer("topic1"),
+        am::allocate_buffer("payload1+"),
+        am::qos::at_least_once,
+        am::properties{}
+    );
+
+    // send publish_1
+    ep->next_layer().set_write_packet_checker(
+        [&](am::packet_variant wp) {
+            BOOST_TEST(publish_1_q1 == wp);
+        }
+    );
+    {
+        auto ec = ep->send(publish_1_q1, as::use_future).get();
+        BOOST_TEST(!ec);
+    }
+
+    // send publish_2
+    ep->next_layer().set_write_packet_checker(
+        [&](am::packet_variant) {
+            BOOST_TEST(false);
+        }
+    );
+    {
+        auto ec = ep->send(publish_2_q1, as::use_future).get();
+        BOOST_TEST(ec.code() == am::errc::bad_message);
+    }
+    auto pid_opt3 = ep->acquire_unique_packet_id(as::use_future).get();
+    BOOST_TEST(pid_opt3.has_value());
+    BOOST_TEST(*pid_opt3 == 2); // 2 can be resused
+
+    ep->next_layer().set_close_checker({});
+    ep->close(as::use_future).get();
+    guard.reset();
+    th.join();
+}
+
 BOOST_AUTO_TEST_CASE(client_recv) {
     auto version = am::protocol_version::v5;
     as::io_context ioc;
diff --git a/test/unit/ut_ep_store.cpp b/test/unit/ut_ep_store.cpp
index f5b8e625c..a3e1c5ba0 100644
--- a/test/unit/ut_ep_store.cpp
+++ b/test/unit/ut_ep_store.cpp
@@ -1744,4 +1744,43 @@ BOOST_AUTO_TEST_CASE(v5_topic_alias) {
     th.join();
 }
 
+BOOST_AUTO_TEST_CASE(restore_packets_error) {
+    auto version = am::protocol_version::v3_1_1;
+    as::io_context ioc;
+    auto guard = as::make_work_guard(ioc.get_executor());
+    std::thread th {
+        [&] {
+            ioc.run();
+        }
+    };
+
+    auto ep = am::endpoint<async_mqtt::role::client, async_mqtt::stub_socket>::create(
+        version,
+        // for stub_socket args
+        version,
+        ioc
+    );
+
+    auto pid_opt1 = ep->acquire_unique_packet_id(as::use_future).get();
+    BOOST_TEST(pid_opt1.has_value());
+    auto publish1 = am::v3_1_1::publish_packet(
+        *pid_opt1,
+        am::allocate_buffer("topic1"),
+        am::allocate_buffer("payload1"),
+        am::qos::at_least_once
+    );
+    as::dispatch(
+        as::bind_executor(
+            ep->strand(),
+            [&] {
+                ep->restore_packets({am::store_packet_variant{publish1}}); // pid is already used
+                auto stored = ep->get_stored_packets();
+                BOOST_TEST(stored.empty());
+            }
+        )
+    );
+    guard.reset();
+    th.join();
+}
+
 BOOST_AUTO_TEST_SUITE_END()