code: def test_add_constant_series(self):
      s = pd.Series([1.0, 2.0, 3.0])
      output = tools.add_constant(s)
      expected = pd.Series([1.0, 1.0, 1.0], name="const")
      assert_series_equal(expected, output["const"])
  
imports: from statsmodels.compat.pandas import assert_frame_equal, assert_series_equal
  from statsmodels.compat.python import lrange
  import string
  import numpy
  from numpy.random import standard_normal
  from numpy.testing import assert_almost_equal, assert_array_equal, assert_equal, assert_string_equal
  import pandas
  import pytest
  from statsmodels.datasets import longley
  from statsmodels.tools import tools
  from statsmodels.tools.tools import pinv_extended
label_desc: Use image node_id 5 for calling the TestTools obj's underlying member method code with example usage: obj.test_add_constant_series() without return types