@Test
public void testPurge() throws Exception {

  assertTrue(
    fileSystemCacheBackend.write( Arrays.asList( directoryKey, key ), value, new HashMap<String, Serializable>() ) );
  assertEquals( fileSystemCacheBackend.read( Arrays.asList( directoryKey, key ) ), value );
  assertTrue( fileSystemCacheBackend.purge( Arrays.asList( directoryKey, key ) ) );
  assertNull( fileSystemCacheBackend.read( Arrays.asList( directoryKey, key ) ) );
}