Testing with Rust

If you look again at the project structure when you create a new Forc project with forc new, you can see a directory called tests/:

$ forc new my-fuel-project
$ cd my-fuel-project
$ tree .
├── Cargo.toml
├── Forc.toml
├── src
│   └── main.sw
└── tests
    └── harness.rs

Note that this is also a Rust package, hence the existence of a Cargo.toml (Rust manifest file) in the project root directory. The Cargo.toml in the root directory contains necessary Rust dependencies to enable you to write Rust-based tests using our Rust SDK, (fuels-rs).

These tests can be run using forc test which will look for Rust tests under the tests/ directory (created automatically with forc new and prepopulated with boilerplate code).

For example, let's write tests against the following contract, written in Sway. This can be done in the pregenerated src/main.sw or in a new file in src. In the case of the latter, update the entry field in Forc.toml to point at the new contract.


abi TestContract {
    fn initialize_counter(value: u64) -> u64;
    #[storage(read, write)]
    fn increment_counter(amount: u64) -> u64;

storage {
    counter: u64 = 0,

impl TestContract for Contract {
    fn initialize_counter(value: u64) -> u64 {
        storage.counter = value;

    #[storage(read, write)]
    fn increment_counter(amount: u64) -> u64 {
        let incremented = storage.counter + amount;
        storage.counter = incremented;

Our tests/harness.rs file could look like:

use fuels::{prelude::*, tx::ContractId};

// Load abi from json
abigen!(TestContract, "out/debug/my-fuel-project-abi.json");

async fn get_contract_instance() -> (TestContract, ContractId) {
    // Launch a local network and deploy the contract
    let wallet = launch_provider_and_get_wallet().await;

    let id = Contract::deploy(

    let instance = TestContract::new(id.to_string(), wallet);

    (instance, id)

async fn can_get_contract_id() {
    let (contract_instance, _id) = get_contract_instance().await;
    // Now you have an instance of your contract you can use to test each function

    let result = contract_instance

    assert_eq!(42, result.value);

    // Call `increment_counter()` method in our deployed contract.
    let result = contract_instance

    assert_eq!(52, result.value);

Then, in the root of our project, running forc test will run the test above, compiling and deploying the contract to a local Fuel network, and calling the ABI methods against the contract deployed in there:

$ forc test
running 1 test
test can_get_contract_id ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.22s