code: def test_banddepth_MBD():
      xx = np.arange(5001) / 5000.0
      y1 = np.zeros(xx.shape)
      y2 = 2 * xx - 1
      y3 = np.ones(xx.shape) * 0.5
      y4 = np.ones(xx.shape) * -0.25
  
      data = np.asarray([y1, y2, y3, y4])
      depth = banddepth(data, method="MBD")
      expected_depth = [
          5.0 / 6,
          (2 * (0.75 - 3.0 / 8) + 3) / 6,
          3.5 / 6,
          (2 * 3.0 / 8 + 3) / 6,
      ]
      assert_almost_equal(depth, expected_depth, decimal=4)
  
file_path: statsmodels/statsmodels/graphics/tests/test_functional.py
imports: import numpy
  from numpy.testing import assert_almost_equal, assert_equal
  import pytest
  from statsmodels.datasets import elnino
  from statsmodels.graphics.functional import banddepth, fboxplot, hdrboxplot, rainbowplot
label_desc: Use image node_id 10 for calling a global function with example usage: test_banddepth_MBD() without return types