How to know/check/confirm/debug if a controller is controlling/working?

edit

Hello everyone,

I am using ROS Melodic and the Gazebo 9. I have been struggling with the controllers for some time now. I have added the gazebo plugin, the intertia and the transmission elements to the urdf.xacro file to simulate the robot in the Gazebo. The problem is when I launch the test_gazebo.launch file the robot is spawned in the gazebo and the simulation is paused, after starting the simulation the robot model just falls down like there is not control whatsoever. It pulled down by the gravity, when I try with the gravity switched off it stays in the position.

my xacro looks like this (I have randomly chosen the fanuc model, it could have been any robot manipulator from the ROS industrial repository):

<robot <a="" href="http://xmlns:xacro="http://wiki.ros.org/xacro%22">xmlns:xacro="http://wiki.ros.org/xacro"> <xacro:include filename="$(find fanuc_resources)/urdf/common_materials.xacro"></xacro:include></robot>

<xacro:macro name="fanuc_m16ib20" params="prefix">

<!--Gazebo ROS Control -->
<gazebo>
    <plugin name="gazebo_ros_control" filename="libgazebo_ros_control.so">
        <robotNamespace>/</robotNamespace>
        <legacyModeNS>true</legacyModeNS>
  </plugin>
</gazebo>

<link name="${prefix}base_link">
  <visual>
        <origin xyz="0 0 0" rpy="0 0 0"/>
        <geometry>
            <mesh filename="package://fanuc_m16ib_support/meshes/m16ib20/visual/base_link.stl"/>
        </geometry>
    <xacro:material_fanuc_yellow />
  </visual>
  <collision>
        <origin xyz="0 0 0" rpy="0 0 0"/>
        <geometry>
            <mesh filename="package://fanuc_m16ib_support/meshes/m16ib20/collision/base_link.stl"/>
        </geometry>
  </collision>
  <inertial>
        <origin xyz = "0.0 0.0 0.0" rpy = "0 0 0" /> 
        <mass value="4.0" />
        <inertia ixx="0.00" iyy="0.00" izz="0.001" ixy="0.0" ixz="0.0" iyz="0.0" />
   </inertial>
</link>
<link name="world"> 
</link>
<joint name="world-${prefix}base_link" type="fixed">
  <origin xyz="0 0 0.0" rpy="0 0 0"/>
  <parent link="world"/>
  <child link="${prefix}base_link"/>
</joint>

<link name="${prefix}base"> 
</link>
<joint name="${prefix}base_link-base" type="fixed">
  <origin xyz="0 0 0.525" rpy="0 0 0"/>
  <parent link="${prefix}base_link"/>
  <child link="${prefix}base"/>
</joint>

<link name="${prefix}link_1">
  <visual>
    <origin xyz="0 0 0" rpy="0 0 0"/>
    <geometry>
      <mesh filename="package://fanuc_m16ib_support/meshes/m16ib20/visual/link_1.stl"/>
    </geometry>
    <xacro:material_fanuc_yellow />
  </visual>
  <collision>
    <origin xyz="0 0 0" rpy="0 0 0"/>
    <geometry>
      <mesh filename="package://fanuc_m16ib_support/meshes/m16ib20/collision/link_1.stl"/>
    </geometry>
  </collision>
  <inertial>
    <origin xyz="0.0 0.0 0.0" rpy="0 0 0"/>
    <mass value="4.0" />
    <inertia ixx="0.00" iyy="0.00" izz="0.001" ixy="0.0" ixz="0.0" iyz="0.0" />
   </inertial>
</link>
<joint name="${prefix}joint_1" type="revolute">
  <origin xyz="0 0 0.525" rpy="0 0 0"/>
  <parent link="${prefix}base_link"/>
  <child link="${prefix}link_1"/>
  <axis xyz="0 0 1 ...