code: def test_subset_2():
      """[Preprocessing | Subset]: assert X is returned for empty subset."""
      sub.set_params(**{"subset": None})
      out = sub.fit_transform(X)
      assert id(out) == id(X)
  
imports: import numpy
  from mlens.preprocessing import Subset, Shift
  from mlens.testing.dummy import Data
label_desc: Use image node_id 2 for calling a global function with example usage: test_subset_2() without return types