new_contents: '''
  Tests of income.py module
  '''
  
  import pytest
  import numpy as np
  from ogusa import income
  
  
  def test_artctan_func():
      '''
      Test of arctan_func()
      '''
      expected_vals = np.array([0.14677821, 0.083305594, 0.057901228])
      xvals = np.array([1, 2, 3])
      a = 1.3
      b = 2.2
      c = 0.5
      test_vals = income.arctan_func(xvals, a, b, c)
  
      assert np.allclose(test_vals, expected_vals)
  
subject: add test of artctan func