code: def test_is_subset():
      assert is_subset(interval(4, 4), interval(3, 7))
      assert is_subset(interval(4, 4), interval(4, 7))
      assert is_subset(interval(4, 7), interval(4, 7))
      assert is_subset(interval(4, 7), interval(3.9, 7))
      assert is_subset(interval(4, np.inf), interval(3, np.inf))
  
      assert not is_subset(interval(4, 9), interval(3.9, 7))
      assert not is_subset(interval(2, 9), interval(3.9, 7))
      assert not is_subset(interval(4, 9), interval(5, 7))
  
file_path: lifelines/lifelines/tests/test_npmle.py
imports: import pytest
  from lifelines.fitters.npmle import npmle, is_subset, create_turnbull_intervals, interval, reconstruct_survival_function
  from numpy import testing
  from lifelines.datasets import load_mice
  from lifelines import KaplanMeierFitter
  import numpy
  import pandas
label_desc: Use image node_id 1 for calling a global function with example usage: test_is_subset() without return types