code: def get_collections_with_limit():
      collections = get_collections()
      m = defaultdict(list)
      for c_name in collections:
          prefix = c_name.split("_")[0]
          if len(m[prefix]) <= 5:
              m[prefix].append(c_name)
      selected_collections = []
      for v in m.values():
          selected_collections.extend(v)
      if len(selected_collections) == 0:
          selected_collections = [None]
      return selected_collections
  
imports: import pytest
  from time import sleep
  from collections import defaultdict
  from pymilvus import connections
  from chaos.checker import InsertChecker, UpsertChecker, FlushChecker, SearchChecker, QueryChecker, IndexCreateChecker, DeleteChecker, Op
  from utils.util_log import test_log
  from chaos import chaos_commons
  from chaos.chaos_commons import assert_statistic
  from common.common_type import CaseLabel
  from chaos import constants
  from utils.util_common import get_collections
  from delayed_assert import assert_expectations
label_desc: Use image node_id 1 for calling a global function with example usage: get_collections_with_limit() and returns: selected_collections