You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: proposal.rs
    path of file: ./repos/ckb/test/src/specs/mining
    
    the code of the file until where you have to start completion: use crate::generic::GetProposalTxIds;
use crate::util::cell::gen_spendable;
use crate::util::transaction::always_success_transaction;
use crate::{Node, Spec};
use ckb_types::prelude::*;

pub struct AvoidDuplicatedProposalsWithUncles;

impl Spec for AvoidDuplicatedProposalsWithUncles {
    // Case: This is not a validation rule, but just an improvement for miner
    //       filling pr
    
    fn run(&self, nodes: &mut Vec<Node>) {
        let node = &nodes[0];
        let cells = gen_spendable(node, 1);
        let tx = always_success_transaction(node, &cells[0]);
        let uncle = {
            let block = node.new_block(None, None, None);
            let uncle = block
                .as_advanced_builder()
                .timestamp((block.timestamp() + 1).pack())
                .set_proposals(vec![tx.proposal_short_id()])
                .build();
            node.submit_block(&block);
            uncle
        };
        node.submit_block(&uncle);
        node.submit_transaction(&tx);

        let block = node.new_block_with_blocking(|template| template.uncles.is_empty());
        assert_eq!(
            vec![uncle.hash()],
            block
                .uncles()
                .into_iter()
                .map(|u| u.hash())
                .collect::<Vec<_>>()
        );
        assert!(
            block.get_proposal_tx_ids().is_empty(),
            "expect empty proposals, actual: {:?}",
            block.get_proposal_tx_ids()
        );
    }