give some time for the discovery for test_on_new_message_callback.

Signed-off-by: Tomoya Fujita <Tomoya.Fujita@sony.com>

Author: Tomoya Fujita

rclpy/test/test_subscription.py

@@ -190,13 +190,31 @@ def test_on_new_message_callback(test_node) -> None:
         qos_profile=10,
         callback=cb)
     pub = test_node.create_publisher(Empty, topic_name, 10)
+
+    # Wait for publisher and subscriber to discover each other
+    max_seconds_to_wait = 5
+    end_time = time.time() + max_seconds_to_wait
+    while sub.get_publisher_count() != 1:
+        time.sleep(0.1)
+        assert time.time() <= end_time  # timeout waiting for pub/sub to discover each other
+
     sub.handle.set_on_new_message_callback(cb)
     cb.assert_not_called()
     pub.publish(Empty())
+
+    # Wait for the callback to be invoked
+    end_time = time.time() + max_seconds_to_wait
+    while cb.call_count == 0 and time.time() <= end_time:
+        time.sleep(0.1)
+
     cb.assert_called_once_with(1)
     sub.handle.clear_on_new_message_callback()
+    cb.reset_mock()
     pub.publish(Empty())
-    cb.assert_called_once()
+
+    # Wait a bit to ensure the message would have been received if callback was still set
+    time.sleep(1.0)
+    cb.assert_not_called()
 
 
 def test_subscription_set_content_filter(test_node) -> None: