Function request_checkpoint 

pub async fn request_checkpoint(
    request_tx: &UnboundedSender<MockExchangeRequest>,
    mocked_exchange: ExchangeId,
    time_request: DateTime<Utc>,
) -> Result<u64, UnindexedClientError>

Asks the MockExchange that reads request_tx to send a VenueCheckpoint on its account stream, with the request stamped time_request.

Answers with the checkpoint’s id once the exchange has sent it, after every account event it produced before it. Sent is not received: a consumer whose account stream ended or lagged before the checkpoint reached it never sees it, and should ask again.

The exchange takes the checkpoint once the request reaches it, whether or not this call is still awaited, so a dropped call can still put a checkpoint on the account stream.

Errors

ConnectivityError::ExchangeOffline for mocked_exchange when the exchange is not running: it never started, or it has stopped.