Make turtle movement detection more robust

Compare min and max positions instead of using assert with initial position (which can fail spuriously if the first pose arrives before the first movement; and also when the turtle reaches the exact same position again).

examples/python-ros2-dataflow/random_turtle.py

@@ -39,6 +39,12 @@ dora_node.merge_external_events(pose_reader)
 
 print("looping", flush=True)
 
+# take track of minimum and maximum coordinates of turtle
+min_x = 1000
+max_x = 0
+min_y = 1000
+max_y = 0
+
 for i in range(500):
     event = dora_node.next()
     if event is None:
@@ -55,8 +61,10 @@ for i in range(500):
         # ROS2 Event
     elif event_kind == "external":
         pose = event.inner()[0].as_py()
-        if i == CHECK_TICK:
-            assert (
-                pose["x"] != 5.544444561004639
-            ), "turtle should not be at initial x axis"
+        min_x = min([min_x, pose["x"]])
+        max_x = max([max_x, pose["x"]])
+        min_y = min([min_y, pose["y"]])
+        max_y = max([max_y, pose["y"]])
         dora_node.send_output("turtle_pose", event.inner())
+
+assert max_x - min_x > 1 or max_y - min_y > 1, "no turtle movement"