fix(mqtt_cxx): Add a simple unit test

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/test/host/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/host/main/CMakeLists.txt

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

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

@@ -0,0 +1,73 @@
+/*
+ * 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"
+
+namespace mqtt = idf::mqtt;
+
+namespace {
+class TestClient final : public mqtt::Client {
+public:
+    using mqtt::Client::Client;
+
+    bool constructed{false};
+    bool connected_called{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);
+        connected_called = true;
+    }
+
+    void on_data(esp_mqtt_event_handle_t const event) override
+    {
+        CHECK(constructed);
+    }
+};
+} // 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://example.com"}},
+        .security = mqtt::Insecure{}
+    };
+    mqtt::ClientCredentials credentials{};
+    mqtt::Configuration config{};
+
+    TestClient client{broker, credentials, config};
+
+    REQUIRE(client.is_started() == false);
+
+    esp_mqtt_event_t event{};
+    event.event_id = MQTT_EVENT_CONNECTED;
+
+    client.dispatch_event_for_test(static_cast<int32_t>(MQTT_EVENT_CONNECTED), &event);
+
+    CHECK(client.connected_called);
+}
+
+extern "C" void app_main(void)
+{
+    Catch::Session session;
+
+    int failures = session.run();
+    if (failures > 0) {
+        printf("TEST FAILED! number of failures=%d\n", failures);
+        exit(1);
+    }
+    printf("Test passed!\n");
+    exit(0);
+}

components/esp_mqtt_cxx/test/host/sdkconfig.defaults

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