public long size() {
    return mInStreamCache.size() + mOutStreamCache.size();
  }
@Test
  public void size() throws Exception {
    StreamCache streamCache = new StreamCache(Constants.HOUR_MS);
    FileInStream is = mock(FileInStream.class);
    FileOutStream os = mock(FileOutStream.class);
    Assert.assertEquals(0, streamCache.size());
    int isId = streamCache.put(is);
    Assert.assertEquals(1, streamCache.size());
    int osId = streamCache.put(os);
    Assert.assertEquals(2, streamCache.size());
    streamCache.invalidate(isId);
    Assert.assertEquals(1, streamCache.size());
    streamCache.invalidate(osId);
    Assert.assertEquals(0, streamCache.size());
  }