code: def test_calculate_normal_reference_bandwidth(self):
      # Should be the same as the Gaussian Kernel
      bw_expected = 0.29781147113698891
      bw = bw_normal_reference(Xi)
      assert_allclose(bw, bw_expected)
  
imports: import numpy
  from scipy import stats
  from statsmodels.sandbox.nonparametric import kernels
  from statsmodels.distributions.mixture_rvs import mixture_rvs
  from statsmodels.nonparametric.bandwidths import select_bandwidth
  from statsmodels.nonparametric.bandwidths import bw_normal_reference
  from numpy.testing import assert_allclose
  import pytest
label_desc: Use image node_id 2 for calling the TestBandwidthCalculation obj's underlying member method code with example usage: obj.test_calculate_normal_reference_bandwidth() without return types