function testTree3_Unaffected() {
  var treeBefore =
      'project()\n' +
      '-order_by(SimpleTable.id ASC)\n' +
      '--select(value_pred(SimpleTable.id gt 100))\n' +
      '---table_access(SimpleTable)\n';

  // Tree should be unaffected, since no index exists on SimpleTable#age.
  lf.testing.treeutil.assertTreeTransformation(
      constructTree1(simpleTable['id'], lf.Order.ASC),
      treeBefore, treeBefore, pass);
}
Tests the case where an OrderByNode exists in the tree, but there is no index
for the column that is used for sorting. The tree should remain unaffected.