public Integer put(FileInStream is) {
    int id = mCounter.incrementAndGet();
    mInStreamCache.put(id, is);
    return id;
  }
@Test
  public void expiration() throws Exception {
    StreamCache streamCache = new StreamCache(0);
    FileInStream is = mock(FileInStream.class);
    FileOutStream os = mock(FileOutStream.class);
    streamCache.put(is);
    streamCache.put(os);
    verify(is).close();
    verify(os).close();
  }