Add test case for ping and pong

This provides a simple example for how to test, and also provides a
staring point for the tests for the logger.

Change-Id: Ieac6858156627c0efcdbb739612e6a4efaf19b80
diff --git a/aos/events/ping_lib.cc b/aos/events/ping_lib.cc
new file mode 100644
index 0000000..31c7b18
--- /dev/null
+++ b/aos/events/ping_lib.cc
@@ -0,0 +1,58 @@
+#include "aos/events/ping_lib.h"
+
+#include "aos/events/pong_generated.h"
+#include "aos/events/ping_generated.h"
+#include "aos/json_to_flatbuffer.h"
+#include "gflags/gflags.h"
+#include "glog/logging.h"
+
+DEFINE_int32(sleep_ms, 10, "Time to sleep between pings");
+
+namespace aos {
+
+namespace chrono = std::chrono;
+
+Ping::Ping(EventLoop *event_loop)
+    : event_loop_(event_loop),
+      sender_(event_loop_->MakeSender<examples::Ping>("/test")) {
+  timer_handle_ = event_loop_->AddTimer([this]() { SendPing(); });
+
+  event_loop_->MakeWatcher(
+      "/test", [this](const examples::Pong &pong) { HandlePong(pong); });
+
+  event_loop_->OnRun([this]() {
+    timer_handle_->Setup(event_loop_->monotonic_now(),
+                         chrono::milliseconds(FLAGS_sleep_ms));
+  });
+
+  event_loop_->SetRuntimeRealtimePriority(5);
+}
+
+void Ping::SendPing() {
+  ++count_;
+  aos::Sender<examples::Ping>::Builder msg = sender_.MakeBuilder();
+  examples::Ping::Builder builder = msg.MakeBuilder<examples::Ping>();
+  builder.add_value(count_);
+  builder.add_send_time(
+      event_loop_->monotonic_now().time_since_epoch().count());
+  CHECK(msg.Send(builder.Finish()));
+  VLOG(2) << "Sending ping";
+}
+
+void Ping::HandlePong(const examples::Pong &pong) {
+  const aos::monotonic_clock::time_point monotonic_send_time(
+      chrono::nanoseconds(pong.initial_send_time()));
+  const aos::monotonic_clock::time_point monotonic_now =
+      event_loop_->monotonic_now();
+
+  const chrono::nanoseconds round_trip_time =
+      monotonic_now - monotonic_send_time;
+
+  if (pong.value() == count_) {
+    VLOG(1) << "Elapsed time " << round_trip_time.count() << " ns "
+            << FlatbufferToJson(&pong);
+  } else {
+    VLOG(1) << "Missmatched pong message";
+  }
+}
+}  // namespace aos