code: def test_banddepth_BD2():
      xx = np.arange(500) / 150.0
      y1 = 1 + 0.5 * np.sin(xx)
      y2 = 0.3 + np.sin(xx + np.pi / 6)
      y3 = -0.5 + np.sin(xx + np.pi / 6)
      y4 = -1 + 0.3 * np.cos(xx + np.pi / 6)
  
      data = np.asarray([y1, y2, y3, y4])
      depth = banddepth(data, method="BD2")
      expected_depth = [0.5, 5.0 / 6, 5.0 / 6, 0.5]
      assert_almost_equal(depth, expected_depth)
  
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 9 for calling a global function with example usage: test_banddepth_BD2() without return types