code: def test_exponential_data_sets_fit():
      N = 20000
      T, C = exponential_survival_data(N, 0.2, scale=10)
      naf = NelsonAalenFitter()
      naf.fit(T, C).plot()
      plt.title("Should be a linear with slope = 0.1")
  
file_path: lifelines/lifelines/tests/test_generate_datasets.py
imports: import os
  import pytest
  import matplotlib.pyplot
  from lifelines import NelsonAalenFitter, KaplanMeierFitter
  from lifelines.generate_datasets import exponential_survival_data
label_desc: Use image node_id 2 for calling a global function with example usage: test_exponential_data_sets_fit() without return types