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with_value

with_value(&value) checks the value the latest delivery lent its handler, on a broker whose deliveries already hold one.

Some brokers decode a delivery in their client and lend the handler that value, such as a database row; the delivery implements Carries<T>. That value never was bytes, so with has nothing to decode; the harness keeps a clone of the lent value instead. The value type needs Clone, PartialEq and Debug. It panics when the latest delivery lent no T: the handler takes another type, or the delivery carried nothing. The row subscription here stands in for such a broker crate: it reads id:name payloads of the in-memory broker as rows (examples/support/carried_rows.rs). received_values returns every lent value, not only the latest.

Example​

examples/testing_subscriber_carried.rs
#[tokio::test]
async fn the_handler_got_the_row() -> Result<(), Box<dyn Error>> {
    let tb = TestApp::start(app()).await?;
    let broker = tb.broker::<MemoryBroker>();
    broker
        .message(&Wire(b"7:alice".to_vec()))
        .to("users")
        .publish()
        .await?;

    broker
        .subscriber("users")
        .assert_called_once()
        .with_value(&Row::new(7, "alice"))
        .settled(HandlerOutcome::ack());
    Ok(())
}