Ros nodes not starting from a launch file

edit

'm trying to create a launch file for starting all the nodes. But for some reason, running the launch file doesn't run the node. The topic in which the node publishes is listed when I run rostopic list, but when I try to echo, nothing is displayed.

On the other hand if I just do a rosrun, it all works perfectly fine.

This is my launch file:

<launch>

  <node pkg="robot_pose_ekf" type="robot_pose_ekf" name="robot_pose_ekf">
    <param name="output_frame" value="odom_combined"/>
    <param name="base_footprint_frame" value="base_footprint"/>
    <param name="freq" value="30.0"/>
    <param name="sensor_timeout" value="1.0"/>
    <param name="odom" value="true"/>
    <param name="imu_data" value="true"/>
    <param name="vo_used" value="true"/> 

 </node>
  <node pkg="IMU_filter" type="test.py" name="test">
  </node>


</launch>

I'm using Indigo. I'm trying to launch a python node in a folder called scripts within the IMU_filter ROS package.