Mailbox test

#[cfg(test)]
mod tests {
    use super::*;
    use std::fs;
    use tempdir::TempDir;

    #[tokio::test]
    async fn test_mailbox_senders() -> Result<(), Box<dyn std::error::Error>> {
        let tmp_dir = TempDir::new("test_mailbox")?;
        let address = tmp_dir.path().join("test_message_1");
        let mut mailbox_sender = MailboxSenders::default();
        let (tx, fut) = mailbox_sender.create(address.clone());
        tx.unbounded_send("foo\n".into())?;
        mailbox_sender
            .get(&address)
            .unwrap()
            .unbounded_send("bar".into())?;
        tx.unbounded_send("baz\n".into())?;
        mailbox_sender.remove(&address);
        drop(tx);
        fut.await?;
        let contents = fs::read_to_string(&address).unwrap();
        assert_eq!(contents, "foo\nbar\nbaz\n");
        Ok(())
    }
}