public void commit() {
            }
        };

        FileListIndexUpdateCallbackImpl callback = new FileListIndexUpdateCallbackImpl(mockCallback, null, 1);
        callback.setMaxDeleteDocumentCacheSize(1000);

        final int threadCount = 10;
        final int urlsPerThread = 100;
        final Thread[] threads = new Thread[threadCount];
        final Exception[] exceptions = new Exception[threadCount];