code: def test_threshold_heuristic():
      # Test for default skip / read heuristic
      # int
      assert threshold_heuristic(1, 9, 1, skip_thresh=8) == "full"
      assert threshold_heuristic(1, 9, 1, skip_thresh=7) is None
      assert threshold_heuristic(1, 9, 2, skip_thresh=16) == "full"
      assert threshold_heuristic(1, 9, 2, skip_thresh=15) is None
      # full slice, smallest step size
      assert (
          threshold_heuristic(slice(0, 9, 1), 9, 2, skip_thresh=2)
          == "full"
      )
      # Dropping skip thresh below step size gives None
      assert (
          threshold_heuristic(slice(0, 9, 1), 9, 2, skip_thresh=1)
          == None
      )
      # As does increasing step size
      assert (
          threshold_heuristic(slice(0, 9, 2), 9, 2, skip_thresh=3)
          == None
      )
      # Negative step size same as positive
      assert (
          threshold_heuristic(slice(9, None, -1), 9, 2, skip_thresh=2)
          == "full"
      )
      # Add a gap between start and end. Now contiguous because of step size
      assert (
          threshold_heuristic(slice(2, 9, 1), 9, 2, skip_thresh=2)
          == "contiguous"
      )
      # To not-contiguous, even with step size 1
      assert (
          threshold_heuristic(slice(2, 9, 1), 9, 2, skip_thresh=1)
          == None
      )
      # Back to full when skip covers gap
      assert (
          threshold_heuristic(slice(2, 9, 1), 9, 2, skip_thresh=4)
          == "full"
      )
      # Until it doesn't cover the gap
      assert (
          threshold_heuristic(slice(2, 9, 1), 9, 2, skip_thresh=3)
          == "contiguous"
      )
  
imports: import time
  from functools import partial
  from io import BytesIO
  from itertools import product
  from threading import Lock, Thread
  import numpy
  import pytest
  from numpy.testing import assert_array_equal
  from ..fileslice import _positive_slice, _simple_fileslice, calc_slicedefs, canonical_slicers, fileslice, fill_slicer, is_fancy, optimize_read_slicers, optimize_slicer, predict_shape, read_segments, slice2len, slice2outax, slicers2segments, strided_scalar, threshold_heuristic
label_desc: Use image node_id 9 for calling a global function with example usage: test_threshold_heuristic() without return types