Mollusk

Mollusk SVM is a lightweight Rust harness for executing single instructions against compiled BPF programs. Use it when you want instruction-level tests without LiteSVM's full transaction API or a running validator.

Recipe

Quick-reference recipe card - copy-paste ready.

use mollusk_svm::Mollusk;
use solana_sdk::instruction::{AccountMeta, Instruction};
 
let mollusk = Mollusk::new(&program_id, "target/deploy/my_program.so");
let result = mollusk.process_instruction(&ix, &account_store);
assert!(result.program_result.is_ok());

When to reach for this:

• Native Rust program development without Anchor TS.
• Benchmarking instruction CU usage in tests.
• Validating account ordering independent of client SDK.
• Quick regression on instruction data parsing.

Working Example

use mollusk_svm::{Mollusk, result::Check};
use solana_sdk::{
    account::Account,
    instruction::{AccountMeta, Instruction},
    pubkey::Pubkey,
};
 
#[test]
fn process_deposit() {
    let program_id = Pubkey::new_unique();
    let mollusk = Mollusk::new(&program_id, "target/deploy/my_program.so");
 
    let user = Pubkey::new_unique();
    let vault = Pubkey::new_unique();
 
    let accounts = vec![
        (user, Account::default()),
        (vault, Account::default()),
    ];
 
    let ix = Instruction {
        program_id,
        accounts: vec![
            AccountMeta::new(user, true),
            AccountMeta::new(vault, false),
        ],
        data: vec![0], // deposit discriminator
    };
 
    mollusk.process_and_validate_instruction(
        &ix,
        &accounts,
        &[Check::success()],
    );
}

What this demonstrates:

• process_and_validate_instruction runs ix and asserts success checks.
• Account store is explicit tuple list of pubkey + Account state.
• Program path points to target/deploy artifact from cargo build-sbf.

Deep Dive

How It Works

• Mollusk loads ELF and invokes entrypoint with provided accounts.
• Returns detailed execution result including CU consumption.
• Check enum validates success, error codes, and log patterns.
• Composes with Solana SDK types - no RPC layer.

Mollusk vs LiteSVM

Rust Notes

use mollusk_svm::result::Check;
 
mollusk.process_and_validate_instruction(
    &ix,
    &accounts,
    &[
        Check::success(),
        Check::compute_units(45_000..=60_000),
    ],
);

Gotchas

• Empty account data - Default accounts lack discriminator. Fix: Serialize Anchor account data into Account::data.
• Wrong program path - Debug vs release .so mismatch. Fix: Consistent cargo build-sbf profile in CI.
• Signer flags only - is_signer on meta without signature verification in mollusk context. Fix: Pair with LiteSVM tx tests for signature paths.
• Missing owner - Account owner must match expected program for deserialization. Fix: Set account.owner = program_id.
• Token CPI - Need token program loaded in mollusk config. Fix: Add SPL program bytes per mollusk docs.
• Check too strict CU - Upgrades change CU. Fix: Use ranges, not exact values.

Alternatives

FAQs

Related

• LiteSVM - transaction-level tests
• Testing CPIs & PDAs - account graphs
• Program Size & CU Discipline - CU budgets
• Testing Basics - pyramid placement

Stack versions: This page was written for Agave 4.1.1, Solana CLI 3.0.10, Anchor 0.32.1, anchor-lang 0.32.1, Rust 1.91.1, @solana/kit 7.0.0, Surfpool 0.12.0, and LiteSVM 0.6.x.