tests(dds): enable GTest smoke-tests and add async-capable realistic MockDDS with GTest async subscription test

Lts/DDS/DdsUnitTestsPlaceholder/ddsGenericDataTests_gtest.cpp

@@ -1,5 +1,7 @@
 #include <gtest/gtest.h>
 #include "mocks/MockDDS.h"
+#include <mutex>
+#include <condition_variable>
 
 TEST(GenericSmokeGTest, BasicStringOps) {
   std::string s = "MiXeD";
@@ -19,3 +21,35 @@ TEST(GenericSmokeGTest, MockDDSPublishReceive) {
   EXPECT_EQ(payload, "payload42");
   EXPECT_EQ(seq, 1UL);
 }
+
+TEST(GenericSmokeGTest, MockDDSAsyncDelivery) {
+  MockDDS::clear_all();
+  std::mutex mtx;
+  std::condition_variable cv;
+  bool received = false;
+  std::string last;
+
+  auto cb = [&](const std::string &payload){
+    std::lock_guard<std::mutex> lk(mtx);
+    last = payload;
+    received = true;
+    cv.notify_one();
+  };
+
+  auto sub = MockDDS::subscribe("topic-async", cb);
+  // publish asynchronously with small delay; callback should be invoked
+  MockDDS::publish_async("topic-async", "async-payload", 20);
+
+  std::unique_lock<std::mutex> lk(mtx);
+  if (!cv.wait_for(lk, std::chrono::seconds(2), [&]{ return received; })) {
+    // timeout
+    MockDDS::unsubscribe("topic-async", sub);
+    FAIL() << "Did not receive async callback in time";
+  }
+  MockDDS::unsubscribe("topic-async", sub);
+  // parse annotation
+  auto pos = last.find(':');
+  ASSERT_NE(pos, std::string::npos);
+  auto payload = last.substr(pos + 1);
+  EXPECT_EQ(payload, "async-payload");
+}