code: def test_freq(self):
      dates = pd.DatetimeIndex(
          ["2018-01-01", "2018-01-02", "2018-01-03", "2018-01-05"],
      )
      data = pd.Series([1, 2, 3, 4], index=dates)
      answer = pd.Series([np.nan, 1.0, 0.5, np.nan])
      date_offset = pd.tseries.offsets.DateOffset(days=1)
      primtive_func = self.primitive(freq=date_offset).get_function()
      given_answer = primtive_func(data)
      np.testing.assert_array_equal(given_answer, answer)
  
file_path: featuretools/featuretools/tests/primitive_tests/transform_primitive_tests/test_percent_change.py
imports: import numpy
  import pandas
  from pytest import raises
  from featuretools.primitives import PercentChange
  from featuretools.tests.primitive_tests.utils import PrimitiveTestBase, find_applicable_primitives, valid_dfs
label_desc: Use image node_id 7 for calling the TestPercentChange obj's underlying member method code with example usage: obj.test_freq() without return types