Test case to reproduce transformation error in buoyancy plugin in the graded mode. Based on test in gazebosim/gz-sim#1302.

buoyancy_test_rotated.sdf

<?xml version="1.0" ?>
<sdf version="1.6">
  <world name="center_of_volume">

    <physics name="fast" type="ignored">
      <real_time_factor>0</real_time_factor>
    </physics>
    <plugin
      filename="libignition-gazebo-physics-system.so"
      name="ignition::gazebo::systems::Physics">
    </plugin>
    <plugin
      filename="libignition-gazebo-buoyancy-system.so"
      name="ignition::gazebo::systems::Buoyancy">
		    <!--<uniform_fluid_density>1000</uniform_fluid_density>-->
			<graded_buoyancy>
			 <default_density>1000</default_density>
				<density_change>
					<above_depth>500</above_depth>
					<density>1</density>
				</density_change>
      </graded_buoyancy>
    </plugin>

     <plugin
      filename="ignition-gazebo-user-commands-system"
      name="ignition::gazebo::systems::UserCommands">
    </plugin>
    <plugin
      filename="ignition-gazebo-scene-broadcaster-system"
      name="ignition::gazebo::systems::SceneBroadcaster">
    </plugin>
    <model name='no_offset'>
      <pose>0 0 0 0 0 0</pose>
      <link name='link'>
        <pose>0 0 0 0 0 0</pose>
        <inertial>
          <pose>0 0 0 0 0 0</pose>
          <inertia>
            <ixx>166.66</ixx>
            <ixy>0</ixy>
            <ixz>0</ixz>
            <iyy>166.66</iyy>
            <iyz>0</iyz>
            <izz>166.66</izz>
          </inertia>
          <mass>1000.0</mass>
        </inertial>
        <visual name='visual'>
          <pose>0 0 0 0 0 0</pose>
          <geometry>
            <box>
              <size>1.0 1.0 1.0</size>
            </box>
          </geometry>
        </visual>
        <collision name='collision'>
          <pose>0 0 0 0 0 0</pose>
          <geometry>
            <box>
              <size>1.0 1.0 1.0</size>
            </box>
          </geometry>
        </collision>
      </link>
    </model>

    <model name='no_offset_rotated'>
      <pose>-3 0 0 0.1 0.2 0.3</pose>
      <link name='link'>
        <pose>0 0 0 0 0 0</pose>
        <inertial>
          <pose>0 0 0 0 0 0</pose>
          <inertia>
            <ixx>166.66</ixx>
            <ixy>0</ixy>
            <ixz>0</ixz>
            <iyy>166.66</iyy>
            <iyz>0</iyz>
            <izz>166.66</izz>
          </inertia>
          <mass>1000.0</mass>
        </inertial>
        <visual name='visual'>
          <pose>0 0 0 0 0 0</pose>
          <geometry>
            <box>
              <size>1.0 1.0 1.0</size>
            </box>
          </geometry>
        </visual>
        <collision name='collision'>
          <pose>0 0 0 0 0 0</pose>
          <geometry>
            <box>
              <size>1.0 1.0 1.0</size>
            </box>
          </geometry>
        </collision>
      </link>
    </model>

    <model name='com_cov_offset'>
      <pose>0 3 0 0 0 0</pose>
      <link name='link'>
        <pose>0 0 0 0 0 0</pose>
        <inertial>
          <pose>1 1 1 0 0 0</pose>
          <inertia>
            <ixx>166.66</ixx>
            <ixy>0</ixy>
            <ixz>0</ixz>
            <iyy>166.66</iyy>
            <iyz>0</iyz>
            <izz>166.66</izz>
          </inertia>
          <mass>1000.0</mass>
        </inertial>
        <visual name='visual'>
          <pose>1 1 1 0 0 0</pose>
          <geometry>
            <box>
              <size>1.0 1.0 1.0</size>
            </box>
          </geometry>
        </visual>
        <collision name='collision'>
          <pose>1 1 1 0 0 0</pose>
          <geometry>
            <box>
              <size>1.0 1.0 1.0</size>
            </box>
          </geometry>
        </collision>
      </link>
    </model>

    <model name='com_cov_offset_rotated'>
      <pose>-3 3 0 0.1 0.2 0.3</pose>
      <link name='link'>
        <pose>0 0 0 0 0 0</pose>
        <inertial>
          <pose>1 1 1 0 0 0</pose>
          <inertia>
            <ixx>166.66</ixx>
            <ixy>0</ixy>
            <ixz>0</ixz>
            <iyy>166.66</iyy>
            <iyz>0</iyz>
            <izz>166.66</izz>
          </inertia>
          <mass>1000.0</mass>
        </inertial>
        <visual name='visual'>
          <pose>1 1 1 0 0 0</pose>
          <geometry>
            <box>
              <size>1.0 1.0 1.0</size>
            </box>
          </geometry>
        </visual>
        <collision name='collision'>
          <pose>1 1 1 0 0 0</pose>
          <geometry>
            <box>
              <size>1.0 1.0 1.0</size>
            </box>
          </geometry>
        </collision>
      </link>
    </model>

  </world>
</sdf>