@Test
public void testGet() {

    Series<String> s = new OffsetLagSeries<>(Series.forData("a", "b", "c", "d"), -1, "X");
    assertThrows(ArrayIndexOutOfBoundsException.class, () -> s.get(-1));
    assertEquals("b", s.get(0));
    assertEquals("c", s.get(1));
    assertEquals("d", s.get(2));
    assertEquals("X", s.get(3));
    assertThrows(ArrayIndexOutOfBoundsException.class, () -> s.get(4));
}