code: def test_color():
      # very weak tests.
      img = np.zeros((20, 21, 3))
      img[:10, :10, 0] = 1
      img[10:, :10, 1] = 1
      img[10:, 10:, 2] = 1
      seg = felzenszwalb(img, sigma=0)
      # we expect 4 segments:
      assert_equal(len(np.unique(seg)), 4)
      assert_array_equal(seg[:10, :10], 0)
      assert_array_equal(seg[10:, :10], 2)
      assert_array_equal(seg[:10, 10:], 1)
      assert_array_equal(seg[10:, 10:], 3)
  
file_path: scikit-image/skimage/segmentation/tests/test_felzenszwalb.py
imports: import numpy
  from skimage import data
  from skimage.segmentation import felzenszwalb
  from skimage._shared import testing
  from skimage._shared.testing import assert_greater, run_in_parallel, assert_equal, assert_array_equal, assert_warns, assert_no_warnings
label_desc: Use image node_id 4 for calling a global function with example usage: test_color() without return types