code: def test_density(self):
      x = array([1, 2, 3, 1, 2, 3, 1, 2, 3])
      y = array([1, 1, 1, 2, 2, 2, 3, 3, 3])
      H, xed, yed = histogram2d(
          x, y, [[1, 2, 3, 5], [1, 2, 3, 5]], density=True
      )
      answer = array([[1, 1, 0.5], [1, 1, 0.5], [0.5, 0.5, 0.25]]) / 9.0
      assert_array_almost_equal(H, answer, 3)
  
imports: from numpy.testing import assert_equal, assert_array_equal, assert_array_max_ulp, assert_array_almost_equal, assert_raises, assert_
  from numpy import arange, add, fliplr, flipud, zeros, ones, eye, array, diag, histogram2d, tri, mask_indices, triu_indices, triu_indices_from, tril_indices, tril_indices_from, vander
  import numpy
  import pytest
label_desc: Use image node_id 3 for calling the TestHistogram2d obj's underlying member method code with example usage: obj.test_density() without return types