Message's private PhantomData<T> makes it difficult to unit test my code

[chamons]

I would like to do something like this in my application code:

pub struct FetchedMessage {
    pub message: Message<MessagePayload>,
    pub is_priority: bool,
}

#[async_trait]
impl PulsarConnection for TestPulsarConnection {
    async fn fetch(&self) -> Result<Option<FetchedMessage>, pulsar::Error> {}
    async fn ack(&self, message: FetchedMessage) -> Result<(), ConsumerError> {
        panic!()
    }
    async fn nack(&self, message: FetchedMessage) -> Result<(), ConsumerError> {
        panic!();
    }
    async fn shutdown(&self, worker_shutdown: impl Future<Output = ()> + Send) {}
}

In my tests, so I could stub out all of the pulsar connection code from my unit tests and test some rare cases.

However, I can not do this because this is the type returned by the pulsar consumer APIs:

https://github.com/streamnative/pulsar-rs/blob/master/src/consumer/message.rs#L9-L20

There is no way to construct it, as it both:

• Does not have a public construction function
• Contains a field that is not public (_phantom)

Could we possible relax one of these two constraints so I can write my tests?