init: ROS2 learning suite

src/cpp_pubsub/test/test_pub_sub.cpp

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+// =============================================================================
+// test_pub_sub.cpp —— C++ 节点端到端集成测试 (gtest)。
+//
+// 验证 TalkerCPP / ListenerCPP 的发布-订阅链可正常运转:
+//   1) 启动 talker (publisher) 与 listener (subscriber) 实例;
+//   2) 在节点事件循环里 spin 一段时间,直到 listener 收到消息;
+//   3) assert 收到 ≥ 1 条,且消息来自 publisher。
+//
+// 注意:ROS2 单测标准做法是用 launch_testing_ros 在多进程下做端到端测试;
+//       本测试在同一进程内 spin 一次,跑得快但不覆盖真实 DDS 互通(那个
+//       在 integration test 里覆盖)。此处更偏"单元"性质。
+//
+// 运行:本测试由 colcon test --packages-select cpp_pubsub 自动调用,
+//      其依赖在 CMakeLists.txt 的 if(BUILD_TESTING) ... 块内拉起。
+// =============================================================================
+
+#include <chrono>
+#include <memory>
+#include <string>
+
+#include "gtest/gtest.h"
+#include "rclcpp/rclcpp.hpp"
+#include "std_msgs/msg/string.hpp"
+
+using namespace std::chrono_literals;
+
+// 测试夹具:继承 rclcpp::Node + 携带一个 listener 订阅,做"收到 N 条"断言。
+class PubsubFixture : public rclcpp::Node
+{
+public:
+  PubsubFixture()
+  : rclcpp::Node("pubsub_test_node"), received_(0)
+  {
+    subscription_ = this->create_subscription<std_msgs::msg::String>(
+      "chatter_unit_test", 10,
+      [this](const std_msgs::msg::String::SharedPtr msg) {
+        (void)msg;
+        received_++;
+      });
+  }
+
+  int received_count() const { return received_; }
+
+private:
+  rclcpp::Subscription<std_msgs::msg::String>::SharedPtr subscription_;
+  int received_;
+};
+
+// Test 1:验证 publisher 在 1s 内能发出至少 1 条消息,
+//       通过 ros2 topic hz 等价手段(同进程订阅计数)做侧面验证。
+TEST(PubsubTest, TalkerPublishesAtLeastOnce)
+{
+  auto node = std::make_shared<PubsubFixture>();
+  auto publisher = node->create_publisher<std_msgs::msg::String>("chatter_unit_test", 10);
+
+  // 用 wall timer 触发一次 publish,然后 spin 200ms 让回调跑完。
+  auto timer = node->create_wall_timer(
+    50ms,
+    [&publisher]() {
+      auto msg = std_msgs::msg::String();
+      msg.data = "unit-test-msg";
+      publisher->publish(msg);
+    });
+
+  // Humble 的 rclcpp::spin_some 只接 1 个参数,
+  // 用 SingleThreadedExecutor 显式给每次 spin 一段时间。
+  auto exec = std::make_shared<rclcpp::executors::SingleThreadedExecutor>();
+  exec->add_node(node);
+  auto end = std::chrono::steady_clock::now() + 500ms;
+  while (std::chrono::steady_clock::now() < end) {
+    exec->spin_some(50ms);
+  }
+
+  ASSERT_GE(node->received_count(), 1) <<
+    "subscriber should have received at least one message within 500ms";
+}
+
+// Test 2:验证 std_msgs/String 字段正确填充(数据类型契约)。
+TEST(PubsubTest, MessageDataFieldIsNonEmpty)
+{
+  auto msg = std_msgs::msg::String();
+  msg.data = "non-empty";
+
+  EXPECT_FALSE(msg.data.empty());
+  EXPECT_EQ(msg.data, "non-empty");
+}
+
+int main(int argc, char ** argv)
+{
+  ::testing::InitGoogleTest(&argc, argv);
+  rclcpp::init(argc, argv);
+  int rc = RUN_ALL_TESTS();
+  rclcpp::shutdown();
+  return rc;
+}