code: def ensure(arg1, arg2=None):
      
  
      assert (isinstance(arg1, str) and isfunction(arg2)) or (isfunction(arg1) and arg2 is None)
  
      description = ""
      predicate = lambda x: x
  
      if isinstance(arg1, str):
          description = arg1
          predicate = arg2
      else:
          description = get_function_source(arg1)
          predicate = arg1
  
      return condition(description, predicate, False, True)
docs: Specify a precondition described by `description` and tested by
      `predicate`.