function testCopy_Simple() {
  var expectedTree =
      'combined_pred_and\n' +
      '-value_pred(Employee.salary gte 200)\n' +
      '-value_pred(Employee.salary lte 600)\n';

  var original = /** @type {!lf.pred.PredicateNode} */ (
      lf.op.and(e.salary.gte(200), e.salary.lte(600)));
  var copy = original.copy();
  assertTreesIdentical(expectedTree, original, copy);
  assertEquals(original.getId(), copy.getId());
}
Tests that copy() creates an identical tree where each node is a new
instance.