docstr: Test ball footprints
docstr_tok: ["Test","ball","footprints"]
code: def test_footprint_ball(self):
      """Test ball footprints"""
      self.strel_worker_3d(
          "data/disk-matlab-output.npz", footprints.ball
      )
  
imports: import numpy
  import pytest
  from numpy.testing import assert_equal
  from skimage._shared.testing import fetch
  from skimage.morphology import footprints
label_desc: Use image node_id 8 for calling the TestFootprints obj's underlying member method code with example usage: obj.test_footprint_ball() without return types