code: def test_sofm_gaussian_df_zero_std(self):
      actual_output = gaussian_df(np.arange(-3, 4), mean=0, std=0)
      expected_output = np.array([0, 0, 0, 1, 0, 0, 0])
      np.testing.assert_array_almost_equal(
          expected_output, actual_output
      )
  
imports: import math
  import numpy
  from neupy import algorithms
  from neupy.exceptions import WeightInitializationError
  from neupy.algorithms.competitive import sofm
  from neupy.algorithms.competitive.neighbours import gaussian_df
  from base import BaseTestCase
label_desc: Use image node_id 1 for calling the SOFMUtilsFunctionTestsCase obj's underlying member method code with example usage: obj.test_sofm_gaussian_df_zero_std() without return types