code: def test_fold_optimization_append():
      assert (
          h2o.is_expr_optimizations_enabled()
      ), "Expression optimization needs to be enabled"
  
      data = single_column_frame()
      data["col_1"] = 1
      data["col_2"] = 2
  
      expr = data._ex
      assert expr._op == "append"
      assert len(expr._children) == 1 + 2 + 2
      assert expr._children[1:] == (1, "col_1", 2, "col_2")
  
file_path: h2o-3/h2o-py/tests/testdir_misc/pyunit_expr_optimizations.py
imports: import h2o
  import sys
  from tests import pyunit_utils
  from h2o import H2OFrame
  from h2o.expr import ExprNode
label_desc: Use image node_id 5 for calling a global function with example usage: test_fold_optimization_append() without return types