def METHOD_NAME(self):
    cuis_to_keep = {'C0000039'} # Because of transition 2 will be kept
    self.cdb.filter_by_cui(cuis_to_keep=cuis_to_keep)
    assert len(self.cdb.cui2names) == 2
    assert len(self.cdb.name2cuis) == 4
    assert len(self.cdb.snames) == 4