code: def test_fold_optimization_append_expr():
      data_dst = single_column_frame()
      data_src = single_column_frame()
  
      def get_expr():
          return ExprNode(
              "append",
              ExprNode("append", data_dst, data_src, "COL_1"),
              data_src,
              "COL_2",
          )
  
      (expr, _) = _assert_expr_results_eq(get_expr)
  
      assert expr._op == "append", "Operator name should be `append`"
      assert (
          len(expr._children) == 1 + 2 + 2
      ), "2 append calls should be folded into a single call"
      assert expr._children[1:] == (
          data_src._ex,
          "COL_1",
          data_src._ex,
          "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 2 for calling a global function with example usage: test_fold_optimization_append_expr() and returns: ExprNode