### Question:
ArbitraryOutputBuffer implements OutputBuffer { @VisibleForTesting void forceFreeMemory() { memoryManager.close(); } ArbitraryOutputBuffer(
            String taskInstanceId,
            StateMachine<BufferState> state,
            DataSize maxBufferSize,
            Supplier<LocalMemoryContext> systemMemoryContextSupplier,
            Executor notificationExecutor); @Override void addStateChangeListener(StateChangeListener<BufferState> stateChangeListener); @Override boolean isFinished(); @Override double getUtilization(); @Override boolean isOverutilized(); @Override OutputBufferInfo getInfo(); @Override void setOutputBuffers(OutputBuffers newOutputBuffers); @Override ListenableFuture<?> isFull(); @Override void enqueue(List<SerializedPage> pages); @Override void enqueue(int partition, List<SerializedPage> pages); @Override ListenableFuture<BufferResult> get(OutputBufferId bufferId, long startingSequenceId, DataSize maxSize); @Override void acknowledge(OutputBufferId bufferId, long sequenceId); @Override void abort(OutputBufferId bufferId); @Override void setNoMorePages(); @Override void destroy(); @Override void fail(); @Override long getPeakMemoryUsage();  }### Answer:
@Test public void testForceFreeMemory() { ArbitraryOutputBuffer buffer = createArbitraryBuffer(createInitialEmptyOutputBuffers(ARBITRARY), sizeOfPages(10)); for (int i = 0; i < 3; i++) { addPage(buffer, createPage(i)); } OutputBufferMemoryManager memoryManager = buffer.getMemoryManager(); assertTrue(memoryManager.getBufferedBytes() > 0); buffer.forceFreeMemory(); assertEquals(memoryManager.getBufferedBytes(), 0); addPage(buffer, createPage(1)); assertEquals(memoryManager.getBufferedBytes(), 0); }