code: def test_sliding_window_splitter_initial_window_start_with_empty_window_raises_error():
      """Test SlidingWindowSplitter."""
      y = _make_series()
      cv = SlidingWindowSplitter(
          fh=1,
          initial_window=15,
          start_with_window=False,
      )
      message = "`start_with_window` must be True if `initial_window` is given"
      with pytest.raises(ValueError, match=message):
          next(cv.split(y))
  
file_path: sktime/sktime/split/tests/test_slidingwindow.py
imports: import numpy
  import pytest
  from sktime.forecasting.tests._config import TEST_FHS, TEST_FHS_TIMEDELTA, TEST_INITIAL_WINDOW, TEST_STEP_LENGTHS, TEST_WINDOW_LENGTHS, TEST_YS
  from sktime.split import SlidingWindowSplitter
  from sktime.split.base._common import _inputs_are_supported
  from sktime.split.tests.test_split import _check_cv, _get_n_incomplete_windows
  from sktime.utils._testing.series import _make_series
  from sktime.utils.datetime import _coerce_duration_to_int
  from sktime.utils.validation.forecasting import check_fh
label_desc: Use image node_id 4 for calling a global function with example usage: test_sliding_window_splitter_initial_window_start_with_empty_window_raises_error() without return types