@Test
public void joiningShouldNotMutateColNamesOnOriginalTable() {

  Table table1 = createSTUDENT();
  Table table2 = createINSTRUCTOR();
  List<String> originalColumns =
      table2.columns().stream().map(Column::name).collect(Collectors.toList());
  table1.joinOn("Age").inner(true, table2);
  List<String> newColumns =
      table2.columns().stream().map(Column::name).collect(Collectors.toList());
  assertEquals(originalColumns, newColumns);
}