public final void set(int newValue) {
        if (newValue < 0) {
            throw new IllegalArgumentException("new value " + newValue + " < 0");
        }
        INDEX_UPDATER.set(this, newValue);
    }
@Test
    void testSet() {
        i1.set(100);
        assertEquals(100, i1.get());

        try {
            i1.set(-1);
            fail();
        } catch (IllegalArgumentException expected) {
            assertThat(expected.getMessage(), allOf(containsString("new value"), containsString("< 0")));
        }
    }