anchor.diff:  
   RUN apt-get -y install python-dev
   
  +# pro forma; test layer invalidation
  +RUN apt-get install htop
  +
  +ADD Makefile /build/Makefile
  +ADD tox.ini /build/tox.ini
  +ADD pytest.ini /build/pytest.ini
  +ADD setup.py /build/setup.py
  +ADD README.rst /build/README.rst
  +ADD HISTORY.rst /build/HISTORY.rst
  +ADD purkinje /build/purkinje
  +
  +
   # Python
  -RUN pip install -r dev-requirements.txt --download-cache $HOME/.pip-cache --use-mirrors
  -
  +RUN pip install --upgrade -r dev-requirements.txt --download-cache $HOME/.pip-cache --use-mirrors
  +ENTRYPOINT "/bin/bash"
   RUN echo "Installed Python packages:"
   RUN pip freeze
   
  
positive.code: #sudo sh -c 'echo "deb http://dl.google.com/linux/chrome/deb/ stable main" >> /etc/apt/sources.list.d/google.list'
  
  RUN apt-get install make
  ADD Makefile /build/Makefile
  ADD tox.ini /build/tox.ini
  ADD pytest.ini /build/pytest.ini
  ADD setup.py /build/setup.py
  ADD README.rst /build/README.rst
  ADD HISTORY.rst /build/HISTORY.rst
  ADD purkinje /build/purkinje
  #ENTRYPOINT ["/bin/bash", "-c", "cd", "/build", ";", "make"]
  #ENTRYPOINT "date"
  ENTRYPOINT cd /build ; make test
  
negative.code: RUN apt-get -y update
  RUN apt-get -y upgrade
  # RUN apt-get -y install nodejs google-chrome-stable firefox
  RUN apt-get -y install nodejs firefox wget python
  
  # Ubuntu's python-pip throws exception with requests lib
  # see https://bugs.launchpad.net/ubuntu/+source/python-pip/+bug/1306991
  RUN wget https://raw.github.com/pypa/pip/master/contrib/get-pip.py
  RUN python get-pip.py
  
  RUN npm install
  
  