@Test
  public void contentWriteCallbackTests() throws RestServiceException {
    ReadIntoCallback readIntoCallback = new ReadIntoCallback();
    NettyRequest nettyRequest = createNettyRequest(HttpMethod.GET, "/", null, new MockChannel());
    NettyRequest.ReadIntoCallbackWrapper wrapper = nettyRequest.new ReadIntoCallbackWrapper(readIntoCallback);
    NettyRequest.ContentWriteCallback callback = nettyRequest.new ContentWriteCallback(null, true, wrapper);
    long bytesRead = new Random().nextInt(Integer.MAX_VALUE);
    // there should be no problem even though httpContent is null.
    callback.onCompletion(bytesRead, null);
    assertEquals("Bytes read does not match", bytesRead, readIntoCallback.bytesRead);
  }
Does any left over tests for {@link NettyRequest.ContentWriteCallback}
ambry-rest/src/test/java/com/github/ambry/rest/NettyRequestTest.java