fix(mqtt_cxx): Implement simple unit tests

Author: david-cermak

.github/workflows/mqtt_cxx__build.yml

@@ -15,7 +15,7 @@ jobs:
       matrix:
         idf_ver: ["release-v5.1", "release-v5.2", "release-v5.3", "release-v5.4", "release-v5.5"]
         idf_target: ["esp32"]
-        test: [ { app: mqtt-basic, path: "components/esp_mqtt_cxx/examples" }]
+        test: [ { app: mqtt-basic, path: "components/esp_mqtt_cxx/examples" }, { app: test, path: "components/esp_mqtt_cxx/test/host" }]
     runs-on: ubuntu-22.04
     container: espressif/idf:${{ matrix.idf_ver }}
     steps:

components/esp_mqtt_cxx/esp_mqtt_cxx.cpp

@@ -260,18 +260,6 @@ void Client::on_data(esp_mqtt_event_handle_t const event)
 {
 }
 
-void Client::dispatch_event_for_test(int32_t event_id, esp_mqtt_event_t *event)
-{
-    if (event == nullptr) {
-        throw MQTTException(ESP_ERR_INVALID_ARG);
-    }
-    event->event_id = static_cast<esp_mqtt_event_id_t>(event_id);
-    auto err = esp_mqtt_dispatch_custom_event(handler.get(), event);
-    if (err != ESP_OK) {
-        throw MQTTException(err);
-    }
-}
-
 std::optional<MessageID> Client::subscribe(std::string const &topic, QoS qos)
 {
     auto res = esp_mqtt_client_subscribe(handler.get(), topic.c_str(),

components/esp_mqtt_cxx/include/esp_mqtt.hpp

@@ -229,14 +229,6 @@ class Client {
 
     virtual ~Client() = default;
 
-    /**
-    * @brief Test helper to dispatch events without a broker connection
-    *
-    * Intended for unit tests; forwards directly to the internal event handler.
-    */
-    void dispatch_event_for_test(int32_t event_id, esp_mqtt_event_t *event);
-
-
 protected:
     /**
      * @brief Helper type to be used as custom deleter for std::unique_ptr.
@@ -266,13 +258,13 @@ class Client {
     */
     virtual void on_error(const esp_mqtt_event_handle_t event);
     /**
-    * @brief Called if there is an disconnection event
+    * @brief Called if there is a disconnection event
     *
     * @param event mqtt event data
     */
     virtual void on_disconnected(const esp_mqtt_event_handle_t event);
     /**
-    * @brief Called if there is an subscribed event
+    * @brief Called if there is a subscribed event
     *
     * @param event mqtt event data
     */
@@ -284,26 +276,26 @@ class Client {
     */
     virtual void on_unsubscribed(const esp_mqtt_event_handle_t event);
     /**
-    * @brief Called if there is an published event
+    * @brief Called if there is a published event
     *
     * @param event mqtt event data
     */
     virtual void on_published(const esp_mqtt_event_handle_t event);
     /**
-    * @brief Called if there is an before connect event
+    * @brief Called if there is a before connect event
     *
     * @param event mqtt event data
     */
     virtual void on_before_connect(const esp_mqtt_event_handle_t event);
     /**
-    * @brief Called if there is an connected event
+    * @brief Called if there is a connected event
     *
     * @param event mqtt event data
     *
     */
     virtual void on_connected(const esp_mqtt_event_handle_t event) = 0;
     /**
-    * @brief Called if there is an data event
+    * @brief Called if there is a data event
     *
     * @param event mqtt event data
     *

components/esp_mqtt_cxx/test/unit/CMakeLists.txt

@@ -0,0 +1,10 @@
+cmake_minimum_required(VERSION 3.5)
+
+
+include($ENV{IDF_PATH}/tools/cmake/project.cmake)
+if(${IDF_TARGET} STREQUAL "linux")
+    set(EXTRA_COMPONENT_DIRS "../../../../common_components/linux_compat")
+    set(COMPONENTS main)
+endif()
+
+project(esp_mqtt_cxx_host_test)

components/esp_mqtt_cxx/test/unit/README.md

@@ -0,0 +1,24 @@
+# Test basic mqtt_cxx wrapper operations
+
+## Warning: Linux target not supported, this test works only on target
+
+## Example output
+```
+I (588) main_task: Started on CPU0
+I (598) main_task: Calling app_main()
+Randomness seeded to: 374196253
+I (608) mqtt_client_cpp: MQTT_EVENT_BEFORE_CONNECT
+E (618) esp-tls: [sock=54] delayed connect error: Connection reset by peer
+E (618) transport_base: Failed to open a new connection: 32772
+E (618) mqtt_client: Error transport connect
+I (618) mqtt_client_cpp: MQTT_EVENT_ERROR
+E (628) mqtt_client_cpp: Last error reported from esp-tls: 0x8004
+E (628) mqtt_client_cpp: Last error captured as transport's socket errno: 0x68
+I (638) mqtt_client_cpp: Last errno string (Connection reset by peer)
+I (648) mqtt_client_cpp: MQTT_EVENT_DISCONNECTED
+===============================================================================
+All tests passed (6 assertions in 1 test case)
+
+Test passed!
+I (5658) main_task: Returned from app_main()
+```

components/esp_mqtt_cxx/test/unit/main/CMakeLists.txt

@@ -0,0 +1,2 @@
+idf_component_register(SRCS "test_esp_mqtt_cxx.cpp"
+                        WHOLE_ARCHIVE)

components/esp_mqtt_cxx/test/unit/main/idf_component.yml

@@ -0,0 +1,5 @@
+dependencies:
+  espressif/catch2: "^3.4.0"
+  esp_mqtt_cxx:
+    version: "*"
+    override_path: '../../../'

components/esp_mqtt_cxx/test/unit/main/test_esp_mqtt_cxx.cpp

@@ -0,0 +1,92 @@
+/*
+ * SPDX-FileCopyrightText: 2025 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+#include "catch2/catch_session.hpp"
+#include "catch2/catch_test_macros.hpp"
+#include "esp_mqtt.hpp"
+#include "esp_mqtt_client_config.hpp"
+#include "esp_netif.h"
+
+namespace mqtt = idf::mqtt;
+
+namespace {
+class TestClient final : public mqtt::Client {
+public:
+    using mqtt::Client::Client;
+
+    bool constructed{false};
+    bool before_connect{false};
+    bool disconnected{false};
+
+    TestClient(const mqtt::BrokerConfiguration &broker, const mqtt::ClientCredentials &credentials, const mqtt::Configuration &config) :
+        mqtt::Client(broker, credentials, config)
+    {
+        constructed = true;
+    }
+
+private:
+    void on_connected(esp_mqtt_event_handle_t const event) override
+    {
+        CHECK(constructed);
+    }
+
+    void on_data(esp_mqtt_event_handle_t const event) override
+    {
+        CHECK(constructed);
+    }
+
+    void on_before_connect(esp_mqtt_event_handle_t const event) override
+    {
+        CHECK(constructed);
+        before_connect = true;
+    }
+
+    void on_disconnected(const esp_mqtt_event_handle_t event) override
+    {
+        CHECK(constructed);
+        disconnected = true;
+
+    }
+
+};
+} // namespace
+
+TEST_CASE("Client does not auto-start and can dispatch events after construction", "[esp_mqtt_cxx]")
+{
+    mqtt::BrokerConfiguration broker{
+        .address = mqtt::URI{std::string{"mqtt://127.0.0.1:1883"}},
+        .security = mqtt::Insecure{}
+    };
+    mqtt::ClientCredentials credentials{};
+    mqtt::Configuration config{};
+
+    TestClient client{broker, credentials, config};
+
+    REQUIRE(client.is_started() == false);
+
+    // start the client and expect disconnection (reset by peer)
+    // since no server's running on this ESP32
+    client.start();
+    CHECK(client.is_started() == true);
+
+    CHECK(client.before_connect);
+    usleep(10000);
+    CHECK(client.disconnected);
+}
+
+extern "C" void app_main(void)
+{
+    ESP_ERROR_CHECK(esp_netif_init());
+    ESP_ERROR_CHECK(esp_event_loop_create_default());
+
+    Catch::Session session;
+
+    int failures = session.run();
+    if (failures > 0) {
+        printf("TEST FAILED! number of failures=%d\n", failures);
+        return;
+    }
+    printf("Test passed!\n");
+}

components/esp_mqtt_cxx/test/unit/sdkconfig.defaults

@@ -0,0 +1,4 @@
+CONFIG_COMPILER_CXX_EXCEPTIONS=y
+CONFIG_ESP_MAIN_TASK_STACK_SIZE=8192
+CONFIG_LWIP_PPP_SUPPORT=y
+CONFIG_PARTITION_TABLE_SINGLE_APP_LARGE=y