code: def true_x(self):
      return np.array([1, 2, 3, 5, 6, 7, 9, 11, 13, 17, 23])
  
imports: from os.path import dirname, join
  import numpy
  from numpy.testing import assert_array_almost_equal, assert_array_equal
  import pandas
  import pytest
  from sksurv.nonparametric import CensoringDistributionEstimator, SurvivalFunctionEstimator, kaplan_meier_estimator, nelson_aalen_estimator
  from sksurv.testing import FixtureParameterFactory
  from sksurv.util import Surv
label_desc: Use image node_id 2 for calling the SimpleDataKMCases obj's underlying member method code with example usage: obj.true_x() and returns: np