@Test
public void testGetX() {

	list1.addValue(-1L, 10F);
	list1.addValue(-2L, -3F);
	list1.addValue(30L, 3F);
	list1.addValue(2L, -100F);
	list1.addValue(31L, -100F);
	/* expected = [ -1, 30, 31] */
	assertEquals(-1L, list1.getX(0).longValue());
	assertEquals(30L, list1.getX(1).longValue());
	assertEquals(31L, list1.getX(2).longValue());
}