@Test
  public void testRemoveFileClearsIndex() throws Exception {
    CacheKey key = putOneThingInCache();
    mStorage.clearAll();
    assertNull(mCache.getResource(key));
    assertFalse(mCache.hasKeySync(key));
  }
Verify that multiple threads can write to the cache at the same time.
imagepipeline-base/src/test/java/com/facebook/cache/disk/DiskStorageCacheTest.java