anchor.diff:  # Test: Some basic commands.
   RUN which spack
   RUN spack --version
  +RUN spack compiler find
   RUN spack compiler list
   RUN spack compiler list --scope=system
   RUN spack compiler list --scope=user
   RUN spack compilers
  -RUN spack spec netcdf
  +RUN spack spec charliecloud
   
   # Test: Install Charliecloud.
  -RUN spack spec charliecloud+builder
  -RUN spack install charliecloud+builder
  -
  -# Test: Run Spack test suite. Distro package dependencies discovered by trial
  -# and error.
  -#
  -# FIXME: Commented out because the suite fails. Last time I tried, 6 tests
  -# failed and 1 "xfailed".
  -#RUN apt-get install -y \
  -#    python-pkg-resources
  -#RUN spack test
  +RUN spack spec charliecloud+docs
  +RUN spack install charliecloud+docs
   
   # Clean up.
   RUN spack clean --all
  
positive.code: #
  # Note: Spack claims that Python 3 works, but using python3 here fails later
  # with "/usr/bin/env: 'python': No such file or directory".
  RUN apt-get install -y \
      python \
      gcc \
      make \
      git \
      curl
  
  # Packages needed to install Charliecloud with Spack. These are in Spack's
  # Docker example [2] but are not documented as prerequisites [1].
  RUN apt-get install -y \
      g++ \
      unzip
  
  # Certain Spack packages (e.g., tar) puke if they detect themselves being
  # configured as UID 0. This is the override. See issue #540 and [2].
  
negative.code: # ch-test-scope: full
  FROM centos:7
  
  # Note: Spack is a bit of an odd duck testing wise. Because it's a package
  # manager, the key tests we want are to install stuff (this includes the Spack
  