code: def assert_on_branch(branch_name):
      # type: (str) -> None
      
      branch = git.current_branch(refresh=True)
  
      if branch.name != branch_name:
          if context.get('pretend', False):
              log.info("Would assert that you're on a <33>{}<32> branch",
                       branch_name)
          else:
              log.err("You're not on a <33>{}<31> branch!", branch_name)
              sys.exit(1)
docs: Print error and exit if *branch_name* is not the current branch.
  
      Args:
          branch_name (str):
              The supposed name of the current branch.