void serializeUpdateToFile(DocumentUpdate update, String fileName) throws IOException {
            GrowableByteBuffer buf = new GrowableByteBuffer(100, 2.0f);
            update.serialize(DocumentSerializerFactory.createHead(buf));
            buf.flip();

            writeBufferToFile(buf, fileName);
        }
Tests applying and serializing document updates.

@author Einar M R Rosenvinge
document/src/test/java/com/yahoo/document/DocumentUpdateTestCase.java