@Test
public void testPrefixWatch() throws Exception {

    putInitial("Hello", "world");
    Thread.sleep(BLOCKING_DELAY_MS);
    assertEquals("world", mData.get("Hello"));
    putChange("Hello", "Seattle");
    putChange("Goodnight", "moon");
    Thread.sleep(BLOCKING_DELAY_MS);
    assertEquals("Seattle", mData.get("Hello"));
    assertEquals("moon", mData.get("Goodnight"));
    putChange("Hello", null);
    Thread.sleep(BLOCKING_DELAY_MS);
    assertFalse("Delete change", mData.containsKey("Hello"));
}