code: def _tested_posteriors() -> (
      DefaultDict[str, Set[Type[AbstractPosterior]]]
  ):
      return DefaultDict(set)
  
imports: from inspect import isabstract
  from typing import DefaultDict, Iterable, Set, Type
  import pytest
  import gpflow.ci_utils
  from gpflow.posteriors import AbstractPosterior
label_desc: Use image node_id 1 for calling a global function with example usage: _tested_posteriors() and returns: DefaultDict