Merge branch 'feat-outbox-host-test' into 'master'

MR: Mqtt outbox move and small examples fix
See merge request espressif/esp-mqtt!311

.gitlab/ci/test.yml

@@ -34,5 +34,7 @@ host_tests:
         ./build_linux_coverage/host_mqtt_client_test.elf -r junit -o junit.xml
         cd ../mqtt_utils_host_test
         ./build_linux_default/mqtt_utils_host_test.elf
+        cd ../mqtt_outbox_host_test
+        ./build_linux_coverage/mqtt_outbox_host_test.elf
         cd ../..
         gcovr --gcov-ignore-parse-errors -g -k -r . --html coverage.html -x coverage.xml

CMakeLists.txt

@@ -1,4 +1,4 @@
-set(srcs mqtt_client.c lib/mqtt_msg.c lib/mqtt_outbox.c lib/platform_esp32_idf.c)
+set(srcs mqtt_client.c lib/mqtt_msg.c lib/platform_esp32_idf.c)
 
 if(CONFIG_MQTT_PROTOCOL_5)
     list(APPEND srcs lib/mqtt5_msg.c mqtt5_client.c)
@@ -15,3 +15,6 @@ idf_component_register(SRCS "${srcs}"
 
 add_subdirectory(${CMAKE_CURRENT_LIST_DIR}/lib/mqtt_utils)
 target_link_libraries(${COMPONENT_LIB} PUBLIC idf::mqtt::utils)
+
+add_subdirectory(${CMAKE_CURRENT_LIST_DIR}/lib/mqtt_outbox)
+target_link_libraries(${COMPONENT_LIB} PRIVATE idf::mqtt::outbox)

examples/custom_outbox/CMakeLists.txt

@@ -17,4 +17,4 @@ target_sources(${mqtt} PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/main/custom_outbox.cp
 # First we get our dependency
 idf_component_get_property(pthread pthread COMPONENT_LIB)
 # And them we link the components
-target_link_libraries(${mqtt} ${pthread})
+target_link_libraries(${mqtt} PRIVATE ${pthread})

examples/custom_outbox/main/Kconfig.projbuild

@@ -2,7 +2,7 @@ menu "Example Configuration"
 
     config BROKER_URL
         string "Broker URL"
-        default "mqtt://mqtt.eclipseprojects.io"
+        default "mqtt://test.mosquitto.org"
         help
             URL of the broker to connect to
 

examples/mqtt5/main/Kconfig.projbuild

@@ -2,7 +2,7 @@ menu "Example Configuration"
 
     config BROKER_URL
         string "Broker URL"
-        default "mqtt://mqtt.eclipseprojects.io"
+        default "mqtt://test.mosquitto.org"
         help
             URL of the broker to connect to
 

examples/ssl/main/Kconfig.projbuild

@@ -2,7 +2,7 @@ menu "Example Configuration"
 
     config BROKER_URI
         string "Broker URL"
-        default "mqtts://mqtt.eclipseprojects.io:8883"
+        default "mqtts://test.mosquitto.org:8883"
         help
             URL of an mqtt broker which this example connects to.
 

examples/tcp/main/Kconfig.projbuild

@@ -2,7 +2,7 @@ menu "Example Configuration"
 
     config BROKER_URL
         string "Broker URL"
-        default "mqtt://mqtt.eclipseprojects.io"
+        default "mqtt://test.mosquitto.org"
         help
             URL of the broker to connect to
 

examples/ws/main/Kconfig.projbuild

@@ -2,7 +2,7 @@ menu "Example Configuration"
 
     config BROKER_URI
         string "Broker URL"
-        default "ws://mqtt.eclipseprojects.io:80/mqtt"
+        default "ws://test.mosquitto.org:80/mqtt"
         help
             URL of an mqtt broker which this example connects to.
 

examples/wss/main/Kconfig.projbuild

@@ -2,7 +2,7 @@ menu "Example Configuration"
 
     config BROKER_URI
         string "Broker URL"
-        default "wss://mqtt.eclipseprojects.io:443/mqtt"
+        default "wss://test.mosquitto.org:443/mqtt"
         help
             URL of an mqtt broker which this example connects to.
 

lib/mqtt_outbox/CMakeLists.txt

@@ -0,0 +1,9 @@
+set(srcs "${CMAKE_CURRENT_LIST_DIR}/../mqtt_outbox.c")
+
+add_library(mqtt_outbox_lib ${srcs})
+target_include_directories(mqtt_outbox_lib PUBLIC
+    ${CMAKE_CURRENT_LIST_DIR}/../include)
+idf_component_get_property(heap heap COMPONENT_LIB)
+idf_component_get_property(log  log  COMPONENT_LIB)
+target_link_libraries(mqtt_outbox_lib PRIVATE ${heap} ${log})
+add_library(idf::mqtt::outbox ALIAS mqtt_outbox_lib)

test/apps/mqtt/main/Kconfig.projbuild

@@ -2,13 +2,13 @@ menu "ESP-MQTT Unit Test Config"
 
     config MQTT_TEST_BROKER_URI
         string "URI of the test broker"
-        default "mqtt://mqtt.eclipseprojects.io"
+        default "mqtt://test.mosquitto.org"
         help
             URL of an mqtt broker which this test connects to.
 
     config MQTT5_TEST_BROKER_URI
         string "URI of the test broker"
-        default "mqtt://mqtt.eclipseprojects.io"
+        default "mqtt://test.mosquitto.org"
         help
             URL of an mqtt broker which this test connects to.
 endmenu

test/apps/mqtt5/main/Kconfig.projbuild

@@ -2,13 +2,13 @@ menu "ESP-MQTT Unit Test Config"
 
     config MQTT_TEST_BROKER_URI
         string "URI of the test broker"
-        default "mqtt://mqtt.eclipseprojects.io"
+        default "mqtt://test.mosquitto.org"
         help
             URL of an mqtt broker which this test connects to.
 
     config MQTT5_TEST_BROKER_URI
         string "URI of the test broker"
-        default "mqtt://mqtt.eclipseprojects.io"
+        default "mqtt://test.mosquitto.org"
         help
             URL of an mqtt broker which this test connects to.
 endmenu

test/apps/publish_connect_test/main/Kconfig.projbuild

@@ -2,25 +2,25 @@ menu "Example Configuration"
 
     config EXAMPLE_BROKER_SSL_URI
         string "Broker SSL URL"
-        default "mqtts://mqtt.eclipseprojects.io:8883"
+        default "mqtts://test.mosquitto.org:8883"
         help
             URL of an mqtt broker for ssl transport
 
     config EXAMPLE_BROKER_TCP_URI
         string "Broker TCP URL"
-        default "mqtt://mqtt.eclipseprojects.io:1883"
+        default "mqtt://test.mosquitto.org:1883"
         help
             URL of an mqtt broker for tcp transport
 
     config EXAMPLE_BROKER_WS_URI
         string "Broker WS URL"
-        default "ws://mqtt.eclipseprojects.io:80/mqtt"
+        default "ws://test.mosquitto.org:80/mqtt"
         help
             URL of an mqtt broker for ws transport
 
     config EXAMPLE_BROKER_WSS_URI
         string "Broker WSS URL"
-        default "wss://mqtt.eclipseprojects.io:443/mqtt"
+        default "wss://test.mosquitto.org:443/mqtt"
         help
             URL of an mqtt broker for wss transport
 

test/mqtt_outbox_host_test/CMakeLists.txt

@@ -0,0 +1,11 @@
+cmake_minimum_required(VERSION 3.16)
+
+include(${CMAKE_CURRENT_LIST_DIR}/../../cmake/CPM.cmake)
+include(${CMAKE_CURRENT_LIST_DIR}/../../cmake/RapidCheck.cmake)
+
+include($ENV{IDF_PATH}/tools/cmake/project.cmake)
+idf_build_set_property(MINIMAL_BUILD ON)
+list(APPEND EXTRA_COMPONENT_DIRS
+    "$ENV{IDF_PATH}/tools/mocks/freertos/")
+
+project(mqtt_outbox_host_test)

test/mqtt_outbox_host_test/README.md

@@ -0,0 +1,14 @@
+# mqtt_outbox host tests
+
+Isolated host tests for `lib/mqtt_outbox.c`. Tests call the outbox API directly —
+no MQTT client, no transport, no FreeRTOS scheduler required.
+
+## Build and run
+
+```bash
+cd test/mqtt_outbox_host_test
+idf.py --preview set-target linux
+idf.py build
+./build/mqtt_outbox_host_test.elf
+```
+

test/mqtt_outbox_host_test/main/CMakeLists.txt

@@ -0,0 +1,22 @@
+idf_component_register(SRCS "test_main.cpp" "test_outbox.cpp"
+                       INCLUDE_DIRS "."
+                       REQUIRES freertos
+                       WHOLE_ARCHIVE)
+
+set(SANITIZER_FLAGS -fsanitize=address,undefined -fno-sanitize-recover=undefined)
+target_compile_options(${COMPONENT_LIB} PRIVATE ${SANITIZER_FLAGS} -Wno-missing-field-initializers)
+target_link_options(${COMPONENT_LIB} INTERFACE ${SANITIZER_FLAGS})
+
+add_subdirectory(${CMAKE_CURRENT_LIST_DIR}/../../../lib/mqtt_outbox
+                 ${CMAKE_CURRENT_BINARY_DIR}/mqtt_outbox)
+
+target_link_libraries(${COMPONENT_LIB} PUBLIC
+    idf::mqtt::outbox
+    Catch2::Catch2WithMain
+    rapidcheck
+    rapidcheck_catch)
+
+if(CONFIG_GCOV_ENABLED)
+    target_compile_options(mqtt_outbox_lib PUBLIC --coverage -fprofile-arcs -ftest-coverage)
+    target_link_options(mqtt_outbox_lib PUBLIC --coverage -fprofile-arcs -ftest-coverage)
+endif()

test/mqtt_outbox_host_test/main/Kconfig

@@ -0,0 +1,9 @@
+menu "Host-test config"
+
+    config GCOV_ENABLED
+        bool "Coverage analyzer"
+        default n
+        help
+            Enables coverage analyzing for host tests.
+
+endmenu

test/mqtt_outbox_host_test/main/idf_component.yml

@@ -0,0 +1,3 @@
+dependencies:
+    espressif/catch2:
+        version: "*"

test/mqtt_outbox_host_test/main/test_main.cpp

@@ -0,0 +1,23 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Unlicense OR CC0-1.0
+ */
+#include <cstdio>
+#include <cstdlib>
+#include <catch2/catch_session.hpp>
+
+extern "C" void app_main(void)
+{
+    int argc = 1;
+    const char *argv[2] = {"mqtt_outbox_host_test", nullptr};
+    int result = Catch::Session().run(argc, argv);
+
+    if (result != 0) {
+        printf("Test failed with result %d\n", result);
+        exit(1);
+    } else {
+        printf("Test passed.\n");
+        exit(0);
+    }
+}

test/mqtt_outbox_host_test/main/test_outbox.cpp

@@ -0,0 +1,356 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Unlicense OR CC0-1.0
+ *
+ * Isolated host tests for lib/mqtt_outbox.c.
+ * All outbox API functions are called directly — no MQTT client, no transport,
+ * no network stack required.
+ */
+#include <exception>
+#include <catch2/catch_test_macros.hpp>
+#include <rapidcheck.h>
+#include <rapidcheck/catch.h>
+#include <algorithm>
+#include <cstdint>
+#include <cstring>
+#include <memory>
+#include <numeric>
+#include <string>
+#include <vector>
+
+extern "C" {
+#include "mqtt_outbox.h"
+}
+
+struct OutboxGuard {
+    explicit OutboxGuard() : handle(outbox_init())
+    {
+        REQUIRE(handle != nullptr);
+    }
+    ~OutboxGuard()
+    {
+        outbox_destroy(handle);
+    }
+    OutboxGuard(const OutboxGuard &) = delete;
+    OutboxGuard &operator=(const OutboxGuard &) = delete;
+
+    outbox_handle_t handle;
+};
+
+static outbox_message_t make_msg(int msg_id, int qos, int msg_type,
+                                 const char *payload, int len)
+{
+    outbox_message_t message{};
+    message.msg_id   = msg_id;
+    message.msg_qos  = qos;
+    message.msg_type = msg_type;
+    message.data     = reinterpret_cast<uint8_t *>(const_cast<char *>(payload));
+    message.len      = len;
+    message.remaining_data = nullptr;
+    message.remaining_len  = 0;
+    return message;
+}
+
+TEST_CASE("Outbox lifecycle")
+{
+    SECTION("init returns a non-null handle") {
+        outbox_handle_t outbox = outbox_init();
+        REQUIRE(outbox != nullptr);
+        outbox_destroy(outbox);
+    }
+    SECTION("destroy on a non-empty outbox reclaims all items") {
+        OutboxGuard outbox;
+        auto message = make_msg(1, 1, 3, "hello", 5);
+        REQUIRE(outbox_enqueue(outbox.handle, &message, 0) != nullptr);
+        // destructor calls outbox_destroy — LSan catches leaks if it is omitted
+    }
+}
+
+TEST_CASE("Outbox enqueue")
+{
+    OutboxGuard outbox;
+    SECTION("enqueued item starts in QUEUED state") {
+        auto message = make_msg(42, 1, 3, "data", 4);
+        outbox_item_handle_t item = outbox_enqueue(outbox.handle, &message, 0);
+        REQUIRE(item != nullptr);
+        REQUIRE(outbox_item_get_pending(item) == QUEUED);
+    }
+    SECTION("size increases by item length after enqueue") {
+        REQUIRE(outbox_get_size(outbox.handle) == 0);
+        const char payload[] = "hello";
+        auto message = make_msg(1, 1, 3, payload, static_cast<int>(sizeof(payload) - 1));
+        outbox_enqueue(outbox.handle, &message, 0);
+        REQUIRE(outbox_get_size(outbox.handle) == sizeof(payload) - 1);
+    }
+    SECTION("multiple enqueues accumulate size") {
+        auto message1 = make_msg(1, 1, 3, "abc", 3);
+        auto message2 = make_msg(2, 1, 3, "de",  2);
+        outbox_enqueue(outbox.handle, &message1, 0);
+        outbox_enqueue(outbox.handle, &message2, 0);
+        REQUIRE(outbox_get_size(outbox.handle) == 5);
+    }
+}
+
+TEST_CASE("Outbox FIFO dequeue")
+{
+    OutboxGuard outbox;
+    SECTION("dequeue returns items in enqueue order") {
+        auto message1 = make_msg(10, 1, 3, "first",  5);
+        auto message2 = make_msg(20, 1, 3, "second", 6);
+        auto message3 = make_msg(30, 1, 3, "third",  5);
+        outbox_enqueue(outbox.handle, &message1, 0);
+        outbox_enqueue(outbox.handle, &message2, 0);
+        outbox_enqueue(outbox.handle, &message3, 0);
+        uint16_t id;
+        int type, qos;
+        size_t len;
+        outbox_item_handle_t item1 = outbox_dequeue(outbox.handle, QUEUED, nullptr);
+        REQUIRE(item1 != nullptr);
+        outbox_item_get_data(item1, &len, &id, &type, &qos);
+        REQUIRE(id == 10);
+        // promote first item so next dequeue skips it
+        outbox_set_pending(outbox.handle, 10, TRANSMITTED);
+        outbox_item_handle_t item2 = outbox_dequeue(outbox.handle, QUEUED, nullptr);
+        REQUIRE(item2 != nullptr);
+        outbox_item_get_data(item2, &len, &id, &type, &qos);
+        REQUIRE(id == 20);
+    }
+    SECTION("dequeue returns nullptr when no item matches state") {
+        auto message = make_msg(1, 1, 3, "x", 1);
+        outbox_enqueue(outbox.handle, &message, 0);
+        REQUIRE(outbox_dequeue(outbox.handle, TRANSMITTED, nullptr) == nullptr);
+        REQUIRE(outbox_dequeue(outbox.handle, ACKNOWLEDGED, nullptr) == nullptr);
+    }
+    SECTION("dequeue on empty outbox returns nullptr") {
+        REQUIRE(outbox_dequeue(outbox.handle, QUEUED, nullptr) == nullptr);
+    }
+}
+
+TEST_CASE("Outbox state transitions")
+{
+    OutboxGuard outbox;
+    SECTION("set_pending changes the state of an item") {
+        auto message = make_msg(5, 1, 3, "msg", 3);
+        outbox_enqueue(outbox.handle, &message, 0);
+        REQUIRE(outbox_set_pending(outbox.handle, 5, TRANSMITTED) == ESP_OK);
+        outbox_item_handle_t item = outbox_dequeue(outbox.handle, TRANSMITTED, nullptr);
+        REQUIRE(item != nullptr);
+        uint16_t id;
+        int type, qos;
+        size_t len;
+        outbox_item_get_data(item, &len, &id, &type, &qos);
+        REQUIRE(id == 5);
+    }
+    SECTION("full state cycle: QUEUED -> TRANSMITTED -> ACKNOWLEDGED -> CONFIRMED") {
+        auto message = make_msg(7, 2, 3, "qos2", 4);
+        outbox_enqueue(outbox.handle, &message, 0);
+        REQUIRE(outbox_set_pending(outbox.handle, 7, TRANSMITTED)  == ESP_OK);
+        REQUIRE(outbox_set_pending(outbox.handle, 7, ACKNOWLEDGED) == ESP_OK);
+        REQUIRE(outbox_set_pending(outbox.handle, 7, CONFIRMED)    == ESP_OK);
+        REQUIRE(outbox_dequeue(outbox.handle, CONFIRMED, nullptr) != nullptr);
+    }
+    SECTION("set_pending on unknown msg_id returns ESP_FAIL") {
+        REQUIRE(outbox_set_pending(outbox.handle, 999, TRANSMITTED) == ESP_FAIL);
+    }
+}
+
+TEST_CASE("Outbox concurrent states")
+{
+    OutboxGuard outbox;
+    SECTION("QUEUED head does not shadow a later TRANSMITTED item") {
+        auto message1 = make_msg(1, 1, 3, "first",  5);
+        auto message2 = make_msg(2, 1, 3, "second", 6);
+        outbox_enqueue(outbox.handle, &message1, 0);
+        outbox_enqueue(outbox.handle, &message2, 0);
+        // Promote the second item only
+        outbox_set_pending(outbox.handle, 2, TRANSMITTED);
+        // dequeue(QUEUED) must still return msg 1
+        outbox_item_handle_t queued_item = outbox_dequeue(outbox.handle, QUEUED, nullptr);
+        REQUIRE(queued_item != nullptr);
+        uint16_t id; int type, qos; size_t len;
+        outbox_item_get_data(queued_item, &len, &id, &type, &qos);
+        REQUIRE(id == 1);
+        // dequeue(TRANSMITTED) must return msg 2
+        outbox_item_handle_t transmitted_item = outbox_dequeue(outbox.handle, TRANSMITTED, nullptr);
+        REQUIRE(transmitted_item != nullptr);
+        outbox_item_get_data(transmitted_item, &len, &id, &type, &qos);
+        REQUIRE(id == 2);
+    }
+    SECTION("TRANSMITTED item is not visible to dequeue(QUEUED)") {
+        auto message = make_msg(3, 1, 3, "only", 4);
+        outbox_enqueue(outbox.handle, &message, 0);
+        outbox_set_pending(outbox.handle, 3, TRANSMITTED);
+        REQUIRE(outbox_dequeue(outbox.handle, QUEUED, nullptr) == nullptr);
+    }
+}
+
+TEST_CASE("Outbox lookup by msg_id")
+{
+    OutboxGuard outbox;
+    SECTION("outbox_get returns the correct item") {
+        auto message1 = make_msg(100, 1, 3, "a", 1);
+        auto message2 = make_msg(200, 1, 3, "b", 1);
+        outbox_enqueue(outbox.handle, &message1, 0);
+        outbox_enqueue(outbox.handle, &message2, 0);
+        outbox_item_handle_t item = outbox_get(outbox.handle, 200);
+        REQUIRE(item != nullptr);
+        uint16_t id; int type, qos; size_t len;
+        outbox_item_get_data(item, &len, &id, &type, &qos);
+        REQUIRE(id == 200);
+    }
+    SECTION("outbox_get returns nullptr for unknown msg_id") {
+        auto message = make_msg(1, 1, 3, "x", 1);
+        outbox_enqueue(outbox.handle, &message, 0);
+        REQUIRE(outbox_get(outbox.handle, 999) == nullptr);
+    }
+}
+
+TEST_CASE("Outbox delete by msg_id and type")
+{
+    OutboxGuard outbox;
+    SECTION("deleted item is no longer found") {
+        auto message = make_msg(55, 1, 3, "del", 3);
+        outbox_enqueue(outbox.handle, &message, 0);
+        REQUIRE(outbox_get_size(outbox.handle) == 3);
+        REQUIRE(outbox_delete(outbox.handle, 55, 3) == ESP_OK);
+        REQUIRE(outbox_get(outbox.handle, 55) == nullptr);
+        REQUIRE(outbox_get_size(outbox.handle) == 0);
+    }
+    SECTION("delete with wrong type returns ESP_FAIL") {
+        auto message = make_msg(56, 1, 3, "x", 1);
+        outbox_enqueue(outbox.handle, &message, 0);
+        REQUIRE(outbox_delete(outbox.handle, 56, 99) == ESP_FAIL);
+        REQUIRE(outbox_get(outbox.handle, 56) != nullptr);
+    }
+    SECTION("delete unknown msg_id returns ESP_FAIL") {
+        REQUIRE(outbox_delete(outbox.handle, 9999, 3) == ESP_FAIL);
+    }
+}
+
+TEST_CASE("Outbox delete by item handle")
+{
+    OutboxGuard outbox;
+    SECTION("item is removed and size decreases") {
+        auto message = make_msg(77, 1, 3, "item", 4);
+        outbox_item_handle_t item = outbox_enqueue(outbox.handle, &message, 0);
+        REQUIRE(item != nullptr);
+        REQUIRE(outbox_get_size(outbox.handle) == 4);
+        REQUIRE(outbox_delete_item(outbox.handle, item) == ESP_OK);
+        REQUIRE(outbox_get(outbox.handle, 77) == nullptr);
+        REQUIRE(outbox_get_size(outbox.handle) == 0);
+    }
+}
+
+TEST_CASE("Outbox expiry")
+{
+    OutboxGuard outbox;
+    SECTION("delete_expired removes items older than timeout") {
+        // enqueue with tick=0; current_tick=200, timeout=100 → age=200 > 100
+        auto message1 = make_msg(1, 1, 3, "old",   3);
+        auto message2 = make_msg(2, 1, 3, "fresh", 5);
+        outbox_enqueue(outbox.handle, &message1, 0);
+        outbox_enqueue(outbox.handle, &message2, 150);  // tick=150, age=50 at current_tick=200
+        int deleted = outbox_delete_expired(outbox.handle, 200, 100);
+        REQUIRE(deleted == 1);
+        REQUIRE(outbox_get(outbox.handle, 1) == nullptr);
+        REQUIRE(outbox_get(outbox.handle, 2) != nullptr);
+    }
+    SECTION("delete_single_expired removes exactly one item") {
+        auto message1 = make_msg(10, 1, 3, "old1", 4);
+        auto message2 = make_msg(20, 1, 3, "old2", 4);
+        outbox_enqueue(outbox.handle, &message1, 0);
+        outbox_enqueue(outbox.handle, &message2, 0);
+        // Both are expired at current_tick=500, timeout=100; only one is removed
+        int id = outbox_delete_single_expired(outbox.handle, 500, 100);
+        REQUIRE(id >= 0);
+        // Exactly one item was removed — the other is still present
+        int remaining = (outbox_get(outbox.handle, 10) != nullptr ? 1 : 0)
+                        + (outbox_get(outbox.handle, 20) != nullptr ? 1 : 0);
+        REQUIRE(remaining == 1);
+    }
+    SECTION("delete_expired returns 0 when no items are expired") {
+        auto message = make_msg(1, 1, 3, "fresh", 5);
+        outbox_enqueue(outbox.handle, &message, 1000);
+        int deleted = outbox_delete_expired(outbox.handle, 1050, 100);
+        REQUIRE(deleted == 0);
+    }
+}
+
+// ---------------------------------------------------------------------------
+// Property-based tests
+// ---------------------------------------------------------------------------
+
+TEST_CASE("Outbox size invariant (RapidCheck)")
+{
+    rc::prop("size equals sum of surviving item lengths after arbitrary enqueue/delete",
+    []() {
+        OutboxGuard outbox;
+        // Generate between 1 and 10 items
+        int count = *rc::gen::inRange(1, 11);
+        uint64_t expected_size = 0;
+        std::vector<std::pair<int, int>> items; // {msg_id, len}
+
+        for (int i = 0; i < count; ++i) {
+            int len = *rc::gen::inRange(1, 32);
+            std::string payload(len, 'x');
+            auto message = make_msg(i + 1, 1, 3, payload.c_str(), len);
+            const bool enqueued = outbox_enqueue(outbox.handle, &message, 0) != nullptr;
+            RC_ASSERT(enqueued);
+            items.push_back({i + 1, len});
+            expected_size += len;
+        }
+
+        RC_ASSERT(outbox_get_size(outbox.handle) == expected_size);
+
+        // Randomly delete some items
+        for (auto &[id, len] : items) {
+            bool del = *rc::gen::arbitrary<bool>();
+
+            if (del) {
+                outbox_delete(outbox.handle, id, 3);
+                expected_size -= len;
+            }
+        }
+
+        RC_ASSERT(outbox_get_size(outbox.handle) == expected_size);
+    });
+}
+
+TEST_CASE("Outbox FIFO ordering property (RapidCheck)")
+{
+    rc::prop("dequeue(QUEUED) returns items in exact enqueue order",
+    []() {
+        OutboxGuard outbox;
+        int count = *rc::gen::inRange(1, 16);
+        std::vector<int> msg_ids;
+        msg_ids.reserve(count);
+
+        for (int i = 0; i < count; ++i) {
+            int id = i + 1;
+            msg_ids.push_back(id);
+            std::string payload = "p" + std::to_string(id);
+            auto message = make_msg(id, 1, 3, payload.c_str(),
+                                    static_cast<int>(payload.size()));
+            const bool enqueued = outbox_enqueue(outbox.handle, &message, 0) != nullptr;
+            RC_ASSERT(enqueued);
+        }
+
+        // Drain in order: promote each head item to TRANSMITTED after inspecting it
+        // so the next dequeue(QUEUED) advances to the next item.
+        for (int i = 0; i < count; ++i) {
+            outbox_item_handle_t item = outbox_dequeue(outbox.handle, QUEUED, nullptr);
+            const bool item_valid = item != nullptr;
+            RC_ASSERT(item_valid);
+            uint16_t id; int type, qos; size_t len;
+            outbox_item_get_data(item, &len, &id, &type, &qos);
+            RC_ASSERT(static_cast<int>(id) == msg_ids[i]);
+            // Advance past this item for the next iteration
+            outbox_set_pending(outbox.handle, id, TRANSMITTED);
+        }
+
+        // No more QUEUED items
+        const bool no_queued_items = outbox_dequeue(outbox.handle, QUEUED, nullptr) == nullptr;
+        RC_ASSERT(no_queued_items);
+    });
+}

test/mqtt_outbox_host_test/sdkconfig.ci.coverage

@@ -0,0 +1 @@
+CONFIG_GCOV_ENABLED=y

test/mqtt_outbox_host_test/sdkconfig.defaults

@@ -0,0 +1,8 @@
+CONFIG_IDF_TARGET="linux"
+CONFIG_COMPILER_CXX_EXCEPTIONS=y
+CONFIG_COMPILER_CXX_RTTI=y
+CONFIG_COMPILER_CXX_EXCEPTIONS_EMG_POOL_SIZE=0
+CONFIG_COMPILER_DISABLE_DEFAULT_ERRORS=y
+CONFIG_LOG_COLORS=n
+CONFIG_LOG_DEFAULT_LEVEL_DEBUG=y
+CONFIG_ESP_MAIN_TASK_STACK_SIZE=10000