code: def coxph_smoke_strata():
      heart = h2o.import_file(
          pyunit_utils.locate("smalldata/coxph_test/heart.csv")
      )
      heart["transplant"] = heart["transplant"].asfactor()
      coxph = H2OCoxProportionalHazardsEstimator(
          stratify_by=["transplant"],
          start_column="start",
          stop_column="stop",
      )
      coxph.train(
          x=["age", "surgery", "transplant"],
          y="event",
          training_frame=heart,
      )
  
      assert coxph.model_id != ""
      assert (
          coxph.formula()
          == "Surv(start, stop, event) ~ age + surgery + strata(transplant)"
      ), (
          "Expected formula to be 'Surv(start, stop, event) ~ age + surgery + strata(transplant)' but it was "
          + coxph.formula()
      )
  
      pred = coxph.predict(test_data=heart)
      assert len(pred) == len(heart)
  
imports: import sys
  import h2o
  from tests import pyunit_utils
  from h2o.estimators.coxph import H2OCoxProportionalHazardsEstimator
label_desc: Use image node_id 1 for calling a global function with example usage: coxph_smoke_strata() without return types