code: def test_calculate_scale():
      # Test for special cases in scale calculation
      npa = np.array
      SIAW = SlopeInterArrayWriter
      SAW = SlopeArrayWriter
      # Offset handles scaling when it can
      aw = SIAW(npa([-2, -1], dtype=np.int8), np.uint8)
      assert get_slope_inter(aw) == (1.0, -2.0)
      # Sign flip handles these cases
      aw = SAW(npa([-2, -1], dtype=np.int8), np.uint8)
      assert get_slope_inter(aw) == (-1.0, 0.0)
      aw = SAW(npa([-2, 0], dtype=np.int8), np.uint8)
      assert get_slope_inter(aw) == (-1.0, 0.0)
      # But not when min magnitude is too large (scaling mechanism kicks in)
      aw = SAW(npa([-510, 0], dtype=np.int16), np.uint8)
      assert get_slope_inter(aw) == (-2.0, 0.0)
      # Or for floats (attempts to expand across range)
      aw = SAW(npa([-2, 0], dtype=np.float32), np.uint8)
      assert get_slope_inter(aw) != (-1.0, 0.0)
      # Case where offset handles scaling
      aw = SIAW(npa([-1, 1], dtype=np.int8), np.uint8)
      assert get_slope_inter(aw) == (1.0, -1.0)
      # Can't work for no offset case
      with pytest.raises(WriterError):
          SAW(npa([-1, 1], dtype=np.int8), np.uint8)
      # Offset trick can't work when max is out of range
      aw = SIAW(npa([-1, 255], dtype=np.int16), np.uint8)
      slope_inter = get_slope_inter(aw)
      assert slope_inter != (1.0, -1.0)
  
imports: import itertools
  from io import BytesIO
  from platform import machine, python_compiler
  import numpy
  import pytest
  from numpy.testing import assert_array_almost_equal, assert_array_equal
  from ..arraywriters import ArrayWriter, ScalingError, SlopeArrayWriter, SlopeInterArrayWriter, WriterError, get_slope_inter, make_array_writer
  from ..casting import int_abs, sctypes, shared_range, type_info
  from ..testing import assert_allclose_safely, suppress_warnings
  from ..volumeutils import _dt_min_max, apply_read_scaling, array_from_file
label_desc: Use image node_id 9 for calling a global function with example usage: test_calculate_scale() without return types