public boolean containsInt(final int value)
    {
        return -1 != indexOf(value);
    }
@Test
    void shouldContainCorrectValues()
    {
        final int count = 20;
        IntStream.range(0, count).forEachOrdered(list::addInt);

        for (int i = 0; i < count; i++)
        {
            assertTrue(list.containsInt(i));
        }

        assertFalse(list.containsInt(-1));
        assertFalse(list.containsInt(20));
    }