public void testCheckElementIndex_ok() {
    assertEquals(0, checkElementIndex(0, 1));
    assertEquals(0, checkElementIndex(0, 2));
    assertEquals(1, checkElementIndex(1, 2));
  }

  public void testCheckElementIndex_badSize() {
    assertThrows(IllegalArgumentException.class, () -> checkElementIndex(1, -1));
  }

  public void testCheckElementIndex_negative() {
    IndexOutOfBoundsException expected =