new_contents: """
  This will run tests on all XBlocks in the `xblock.test.v0`
  entrypoint. Did you notice something about that entry point? It ends
  with a v0. That means this is not finished. At some point, we might
  stop running v0 tests, replacing them with test case failures, and
  run v1 tests only.
  
  That be the dragon here.
  """
  import pkg_resources
  
  
  class DuplicateXBlockTest(Exception):
      '''
      This exception is shown if there are multiple entry points with the same
      class name for a test. In most cases, this means you have two versions
      of the same XBlock installed, or two XBlocks with namespace collisions. In
      either case, it'd be nice to resolve (likely by renaming tests as they
      come in, hopefully still being careful to catch collisions which might
      effect deployed XBlocks. See discussion at:
        https://github.com/edx/edx-platform/pull/11032#discussion_r48097392).
      '''
      pass
  
  
  class InvalidTestName(Exception):
      '''
      This means you have an entry point for a test that does not correspond
      to a properly named test class. For example, if you cut-and-paste entry
      points in `setup.py`, and forgot to repoint the class (so it points to
      `DoneXBlock` instead of `TestDone`), or otherwise made an error, you
      will see this exception.
      '''
      pass
  
  xblock_loaded = False  # pylint: disable=invalid-name
  
  for entrypoint in pkg_resources.iter_entry_points(group="xblock.test.v0"):  # pylint: disable=no-member
      plugin = entrypoint.load()
      classname = plugin.__name__
      if classname in globals():
          raise DuplicateXBlockTest(classname)
      if not classname.startswith("Test"):
          raise InvalidTestName("Test class should start with 'Test': " + classname)
      # This should never happen, but while we're testing for class name
      # validity, we figured it was okay to be a little overly defensive.
      # See discussion at:
      # https://github.com/edx/edx-platform/pull/11032#discussion_r48097392
      if not classname.replace("_", "").isalnum():
          raise InvalidTestName("Python variables should be letters, numbers, and underscores: " + classname)
      globals()[classname] = plugin
      print "Loading XBlock test: " + classname
      xblock_loaded = True
  
subject: Allow us to run tests from external XBlock repositories