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: sparse_merkle_test.rs
    path of file: ./repos/diem/storage/diem-scratchpad/src/sparse_merkle
    
    the code of the file until where you have to start completion: // Copyright (c) The Diem Core Contributors
// SPDX-License-Identifier: Apache-2.0

use super::*;
use crate::test_utils::{
    proof_reader::ProofReader,
    proptest_helpers::{arb_smt_correctness_case, test_smt_correctness_impl},
};
use diem_crypto::{
    hash::{CryptoHash, TestOnlyHash, SPARSE_MERKLE_PLACEHOLDER_HASH},
    HashValue,
};
use diem_types::{
    account_state_blob::AccountStateBlob,
    proof::{SparseMerkleLeafNode, SparseMerkleProof},
};
use proptest::prelude::*;

fn update_byte(original_key: &HashValue, n: usize, byte: u8) -> HashValue {
    let mut key = original_key.to_vec();
    key[n] = byte;
    HashValue::from_slice(&key).unwrap()
}

fn hash_internal(left_
    
fn test_insert_at_in_mem_empty() {
    let key1 = HashValue::from_slice(&[0; 32]).unwrap();
    let value1_hash = b"hello".test_only_hash();
    let key2 = update_byte(&key1, 0, 0b01000000);
    let value2_hash = b"world".test_only_hash();

    let key3 = update_byte(&key1, 0, 0b10000000);
    let value3: AccountStateBlob = vec![1, 2, 3].into();

    let internal = SubTree::new_internal(
        SubTree::new_leaf_with_value_hash(key1, value1_hash),
        SubTree::new_leaf_with_value_hash(key2, value2_hash),
    );
    let internal_hash = internal.hash();
    let root = SubTree::new_internal(internal, SubTree::new_empty());
    let smt = SparseMerkleTree::new_with_root(root);

    let root_hash = hash_internal(internal_hash, hash_leaf(key3, value3.hash()));
    let updated = smt
        .batch_update(vec![(key3, &value3)], &ProofReader::default())
        .unwrap();
    assert_eq!(updated.root_hash(), root_hash);
}