public void commit() {
            }
        };

        FileListIndexUpdateCallbackImpl callback = new FileListIndexUpdateCallbackImpl(mockCallback, null, 1);

        // Pre-populate with some URLs
        synchronized (mockCallback) {
            for (int i = 0; i < 100; i++) {
                callback.deleteUrlList.add("http://example.com/doc" + i);
            }
        }