@Override
    public void append(int keyGroup, byte[] value) throws IOException {
        LOG.trace("append to {}: keyGroup={} {} bytes", logId, keyGroup, value.length);
        if (closed) {
            LOG.warn("{} is closed.", logId);
            return;
        }
        activeChangeSet.add(StateChange.ofDataChange(keyGroup, value));
        preEmptiveFlushIfNeeded(value);
    }
@Test
    void testAppend() throws Exception {
        withWriter(
                (writer, uploader) -> {
                    writer.append(KEY_GROUP, getBytes());
                    writer.append(KEY_GROUP, getBytes());
                    writer.append(KEY_GROUP, getBytes());
                    assertNoUpload(uploader, "append shouldn't persist");
                });
    }