code: def check_backends(title):
      
      path = os.path.dirname(fulltext.backends.__file__)
      errs = []
      for name in os.listdir(path):
          if not name.endswith('.py'):
              continue
          if name == '__init__.py':
              continue
  
          mod_name = "fulltext.backends.%s" % (
              os.path.splitext(os.path.basename(name))[0])
  
          try:
              mod = __import__(mod_name, fromlist=[' '])
          except ImportError as err:
              errs.append((mod_name, str(err)))
              continue
  
          kw = dict(encoding='utf8', encoding_errors='strict',
                    kwargs={})
          try:
              inst = getattr(mod, "Backend")(**kw)
              if hasattr(inst, "check"):
                  inst.check(title=title)
          except Exception as err:
              errs.append((mod.__name__, str(err)))
      if errs:
          for mod, err in errs:
              msg = hilite("%s: %s" % (mod, err), ok=False)
              print(msg, file=sys.stderr)
          sys.exit(1)
docs: Invoke test() for all backends and fail (raise) if some dep
      is missing.