assertThat(keySet).containsExactly(4, 6, 8, 0, 1, 2, 5, 7, 9);
// 4 expires
ticker.advance(1, MILLISECONDS);
assertThat(keySet).containsExactly(6, 8, 0, 1, 2, 5, 7, 9);
ticker.advance(1, MILLISECONDS);
assertThat(keySet).containsExactly(6, 8, 0, 1, 2, 5, 7, 9);
// 6 expires
ticker.advance(1, MILLISECONDS);
assertThat(keySet).containsExactly(8, 0, 1, 2, 5, 7, 9);