code: def test_split_offset_str():
      """Tests splitting offset strings."""
      assert split_offset_str("7D") == ["7", "D"]
      assert split_offset_str("2H") == ["2", "H"]
      assert split_offset_str("+1D") == ["+1", "D"]
      assert split_offset_str("-500D") == ["-500", "D"]
  
imports: import warnings
  from dataclasses import dataclass
  from typing import List
  import numpy
  import pandas
  import pytest
  import scipy
  from greykite.common import constants
  from greykite.common.evaluation import ElementwiseEvaluationMetricEnum
  from greykite.common.python_utils import apply_func_to_columns
  from greykite.common.python_utils import assert_equal
  from greykite.common.python_utils import dictionaries_values_to_lists
  from greykite.common.python_utils import dictionary_values_to_lists
  from greykite.common.python_utils import flatten_list
  from greykite.common.python_utils import get_integer
  from greykite.common.python_utils import get_pattern_cols
  from greykite.common.python_utils import group_strs_with_regex_patterns
  from greykite.common.python_utils import ignore_warnings
  from greykite.common.python_utils import mutable_field
  from greykite.common.python_utils import reorder_columns
  from greykite.common.python_utils import split_offset_str
  from greykite.common.python_utils import unique_dict_in_list
  from greykite.common.python_utils import unique_elements_in_list
  from greykite.common.python_utils import unique_in_list
  from greykite.common.python_utils import update_dictionaries
  from greykite.common.python_utils import update_dictionary
label_desc: Use image node_id 18 for calling a global function with example usage: test_split_offset_str() without return types