public int serialize(String filename, Routable routable) {
        return serialize(filename, routable, data -> data);
    }
Writes the content of the given routable to the given file.

@param filename The name of the file to write to.
@param routable The routable to serialize.
@param tamper allows tampering with serialized data
@return The size of the written file.
documentapi/src/test/java/com/yahoo/documentapi/messagebus/protocol/MessagesTestBase.java