void moveHeadIndexByOne() {
        this.headIndex = (headIndex + 1) % windowSize;
    }
@Test
    public void testMoveHeadIndexByOne() {
        FixedSizeSlidingWindowMetrics metrics = new FixedSizeSlidingWindowMetrics(3);

        assertThat(metrics.headIndex).isZero();

        metrics.moveHeadIndexByOne();

        assertThat(metrics.headIndex).isEqualTo(1);

        metrics.moveHeadIndexByOne();

        assertThat(metrics.headIndex).isEqualTo(2);

        metrics.moveHeadIndexByOne();

        assertThat(metrics.headIndex).isZero();

        metrics.moveHeadIndexByOne();

        assertThat(metrics.headIndex).isEqualTo(1);

    }