anchor.diff:  # /opt/ros/${ROS_DISTRO}/share can be changed after rosdep install, so we run it 3 times.
   RUN for i in $(seq 3); do rosdep install --rosdistro ${ROS_DISTRO} -r -y -i --from-paths /opt/ros/${ROS_DISTRO}/share ~/ros/${ROS_DISTRO}/src; done
   
  +ARG TESTING
   RUN if [ ${TESTING} = "true" ] ; then \
         rm -rf ~/ros; \
       else \
  
positive.code: ARG UBUNTU_VERSION
  FROM osrf/ros:${ROS_DISTRO}-desktop-${UBUNTU_VERSION}
  
  ARG ROS_DISTRO
  ARG TESTING
  RUN echo "deb http://packages.ros.org/ros-testing/ubuntu $(lsb_release -sc) main" > /etc/apt/sources.list.d/ros-latest.list
  
  RUN apt-get update && apt-get install -y wget git
  
negative.code:     pip install 'pip<10' && \
      pip install -U setuptools
  
  ARG ROS_DISTRO
  RUN cd ~ && \
      mkdir -p ros/${ROS_DISTRO}/src && \
      cd ros/${ROS_DISTRO}/src && \
  