@Test
public void testRemove() {

    String key = Random.getString();
    Set<Integer> value1 = randomValueSet();
    Set<Integer> value2 = randomValueSet();
    Assert.assertNull(map.remove(key));
    map.put(key, value1);
    Assert.assertEquals(map.remove(key), value1);
    map.put(key, value2);
    Assert.assertEquals(map.remove(key), value2);
}