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: multitoken.rs
    path of file: ./repos/namada/crates/namada/src/ledger/native_vp
    
    the code of the file until where you have to start completion: //! Native VP for multitokens

use std::collections::{BTreeSet, HashMap};

use namada_governance::is_proposal_accepted;
use namada_state::StateRead;
use namada_token::storage_key::is_any_token_parameter_key;
use namada_tx::Tx;
use namada_vp_env::VpEnv;
use thiserror::Error;

use crate::address::{Address, InternalAddress};
use crate::ledger::native_vp::{self, Ctx, NativeVp};
use crate::storage::{Key, KeySeg};
use crate::token::storage_key::{
    is_any_minted_balance_key, is_any_minter_key, is_any_token_balance_key,
    minter_key,
};
use crate::token::Amount;
use crate::vm::WasmCacheAccess;

#[allow(missing_docs)]
#[derive(Error, Debug)]
pub enum Error {
    #[error("Native VP error: {0}")]
    NativeVpError(#[from] native_vp::Error),
}

/// Multitoken functions result
pub type 
    
    fn test_invalid_key_update() {
        let mut state = TestState::default();
        let mut keys_changed = BTreeSet::new();

        let key = Key::from(
            Address::Internal(InternalAddress::Multitoken).to_db_key(),
        )
        .push(&"invalid_segment".to_string())
        .unwrap();
        state
            .write_log_mut()
            .write(&key, 0.serialize_to_vec())
            .expect("write failed");

        keys_changed.insert(key);

        let tx_index = TxIndex::default();
        let tx = dummy_tx(&state);
        let gas_meter = RefCell::new(VpGasMeter::new_from_tx_meter(
            &TxGasMeter::new_from_sub_limit(u64::MAX.into()),
        ));
        let (vp_wasm_cache, _vp_cache_dir) = wasm_cache();
        let verifiers = BTreeSet::new();
        let sentinel = RefCell::new(VpSentinel::default());
        let ctx = Ctx::new(
            &ADDRESS,
            &state,
            &tx,
            &tx_index,
            &gas_meter,
            &sentinel,
            &keys_changed,
            &verifiers,
            vp_wasm_cache,
        );

        let vp = MultitokenVp { ctx };
        assert!(
            !vp.validate_tx(&tx, &keys_changed, &verifiers)
                .expect("validation failed")
        );
    }