code: def test_passthrough_does_not_broadcast_variables():
      """Test that OptionalPassthrough does not itself vectorize/broadcast columns."""
      from sktime.datasets import load_longley
      from sktime.transformations.compose import OptionalPassthrough
      from sktime.transformations.series.detrend import Deseasonalizer
  
      _, X = load_longley()
  
      t = OptionalPassthrough(Deseasonalizer())
      t.fit(X)
  
imports: import pytest
  from sktime.tests.test_switch import run_test_for_class
  from sktime.transformations.compose import OptionalPassthrough
  from sktime.utils.validation._dependencies import _check_soft_dependencies
label_desc: Use image node_id 2 for calling a global function with example usage: test_passthrough_does_not_broadcast_variables() without return types