code: def test_concordance_index_function_exits():
      N = 10 * 1000
      actual_times = np.random.exponential(1, size=N)
      predicted_times = np.random.exponential(1, size=N)
      obs = np.ones(N)
      assert fast_cindex(actual_times, predicted_times, obs)
  
file_path: lifelines/lifelines/tests/utils/test_concordance.py
imports: import pytest
  import numpy
  import pandas
  from lifelines import CoxPHFitter
  from lifelines.datasets import load_rossi
  from lifelines.utils.concordance import concordance_index
  from lifelines.utils.concordance import concordance_index
  from lifelines.utils.concordance import naive_concordance_index
label_desc: Use image node_id 4 for calling a global function with example usage: test_concordance_index_function_exits() without return types