Implement the pure-virtual functions in the Waitable class. (#548)

* Implement the pure-virtual functions in the Waitable class.

Signed-off-by: Chris Lalancette <clalancette@gmail.com>

test_rclcpp/test/test_waitable.cpp

@@ -13,12 +13,24 @@
 // limitations under the License.
 
 #include <chrono>
+#include <cstddef>
+#include <functional>
 #include <future>
 #include <memory>
+#include <stdexcept>
 
 #include "gtest/gtest.h"
 
-#include "rclcpp/rclcpp.hpp"
+#include "rcl/allocator.h"
+#include "rcl/time.h"
+#include "rcl/timer.h"
+
+#include "rclcpp/callback_group.hpp"
+#include "rclcpp/clock.hpp"
+#include "rclcpp/contexts/default_context.hpp"
+#include "rclcpp/executors.hpp"
+#include "rclcpp/node.hpp"
+#include "rclcpp/waitable.hpp"
 
 class WaitableWithTimer : public rclcpp::Waitable
 {
@@ -87,6 +99,11 @@ class WaitableWithTimer : public rclcpp::Waitable
     execute_promise_.set_value(RCL_RET_OK == ret);
   }
 
+  void set_on_ready_callback(std::function<void(size_t, int)>) override {}
+  void clear_on_ready_callback() override {}
+
+  std::shared_ptr<void> take_data_by_entity_id(size_t) override {return nullptr;}
+
   std::shared_ptr<rcl_timer_t> timer_;
   size_t timer_idx_;
   std::promise<bool> execute_promise_;