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How to Set Up Foundry to Test Smart Contracts on Hedera

Foundry provides tools to developers who are developing smart contracts. One of the 3 main components of Foundry is Forge: Foundry’s testing framework. Tests are written in Solidity and are easily run with the forge test command. This tutorial will dive into configuring Foundry with Hedera to use Forge in order to write and run tests for smart contracts.
Note: Hashio, the SwirldsLabs hosted version of the JSON-RPC Relay, is in beta. If issues are encountered while using Foundry and Hashio, please create an issue in the JSON-RPC Relay GitHub repository.


Table of Contents

Create a Hedera Project and Install the Hedera JS SDK

Open your terminal and create a directory called my-hedera-project by running the following command:
mkdir my-hedera-project && cd my-hedera-project
Initialize a node project and accept all defaults:
npm init -y
Install dependencies and the Hedera JavaScript SDK:
npm install --save @hashgraph/sdk
In your project root directory, create your .env file and fill the contents with your account Id and private key from the developer portal where you created your Hedera Testnet account. They will be used to create your Hedera client.
Create a file named index.ts and create your Hedera client.
import { Client, AccountId, PrivateKey, Hbar, TokenId, ContractId } from "@hashgraph/sdk";
import fs from "fs";
import dotenv from "dotenv";
import { deployContract } from "./services/hederaSmatContractService";
// create your client
const accountIdString = process.env.OPERATOR_ACCOUNT_ID;
const privateKeyString = process.env.OPERATOR_PRIVATE_KEY;
if (accountIdString === undefined || privateKeyString === undefined ) { throw new Error('account id and private key in env file are empty')}
const operatorAccountId = AccountId.fromString(accountIdString);
const address = operatorAccountId.toSolidityAddress();
const operatorPrivateKey = PrivateKey.fromString(privateKeyString);
const client = Client.forTestnet().setOperator(operatorAccountId, operatorPrivateKey);
client.setDefaultMaxTransactionFee(new Hbar(100));
In the root directory, create two new empty folders: cache and test. Inside the cache folder, create the subfolder forge-cache. Inside the test folder, create a subfolder called foundry. Your Hedera project directory structure should look similar to this:
├── cache
├── contracts
├── test
├── .env
├── .gitignore
├── index.ts
├── package-lock.json
├── package.json
└── tsconfig.json

Create a Sample Foundry Project

Open a new terminal window and Create a sample Foundry project by running the following command in the new terminal:
forge init <project-name>
Your foundry project will have the following directory structure
├── lib
├── script
├── src
└── test

Copy the lib/forge-std folder from the sample foundry project into your Hedera Project

Foundry manages dependencies using git submodules by default. Hedera manages dependencies through npm modules. The default sample project comes with one dependency installed: Forge Standard Library. We need to get that over to our Hedera project. Copy the lib/forge folder from the sample Foundry project and put it in your Hedera project. Your Hedera project directory structure will look like this:
├── cache
├── contracts
├── lib
├── test
├── .env
├── .gitignore
├── index.ts
├── package-lock.json
├── package.json
└── tsconfig.json

Configure Foundry in your Hedera project

Foundry’s default directory for contracts is src/, but we will need it to map to contracts. Tests will map to our test/foundry path, and the cache_path will map to our cache/forge-cache directory.
Let’s create a Foundry configuration file to update how Foundry behaves. Create a file in the root of your Hedera project and name it foundry.toml and add the following lines:
src = 'contracts'
out = 'out'
libs = ['node_modules', 'lib']
test = 'test/foundry'
cache_path = 'forge-cache'

Remap dependencies

Foundry manages dependencies using git submodules and has the ability to remap them to make them easier to import. Let’s create a new file at the project's root directory called remappings.txt and write the following lines:
And what these remappings translate to is:
  • To import from ds-test we write import “ds-test/TodoList.sol”;
  • To import from forge-std we write import “forge-std/Contract.sol”;

Create Tests

Create a smart contract

Create a smart contract file named TodoList.sol under the contracts directory.
// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.13;
struct Todo {
uint id;
string description;
bool completed;
contract TodoList {
// need to keep count of todos as we insert into map
uint256 public numberOfTodos = 0;
mapping(uint => Todo) public todos;
function createTodo(string memory description) public {
todos[numberOfTodos] = Todo(numberOfTodos, description, false);
function getTodoById(uint256 id) public view returns (Todo memory) {
return todos[id];
function toggleCompleted(uint _id) public {
Todo memory _todo = todos[_id];
_todo.completed = !_todo.completed;
todos[_id] = _todo;

Create tests written in Solidity

Create a file named TodoList.t.sol under test/foundry and write the following test:
// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.13;
import "forge-std/Test.sol";
import "contracts/TodoList.sol";
contract TodoListTest is Test {
TodoList public todoList;
uint256 numberOfTodos;
// Arrange everything you need to run your tests
function setUp() public {
todoList = new TodoList();
function test_CreateTodo() public {
// arrange
todoList.createTodo("Feed my dog");
// act
numberOfTodos = todoList.numberOfTodos();
// assert
assertEq(numberOfTodos, 1);
function test_GetTodoById() public {
// arrange
todoList.createTodo("Pack my bags");
// act
Todo memory todo = todoList.getTodoById(1);
// assert
assertEq(todo.description, "Pack my bags");
function test_ToggleCompleted() public {
// arrange
todoList.createTodo("Update my calendar");
// act
// assert
Todo memory todo = todoList.getTodoById(1);
assertEq(todo.completed, true);

Build and run your tests

In your terminal, ensure you are in your forge project directory and run the following command to build:
forge build
To run your tests run the following command:
forge test

Deploy Your Smart Contract

Step 1: Compile your smart contract using solc

solcjs --bin contracts/TodoList.sol -o binaries

Step 2: Read the compiled bytecode

In your index.ts file import fs in order to read your smart contracts bytecode.
import fs from "fs";
const bytecode = fs.readFileSync("binaries/contracts_ERC20FungibleToken_sol_ERC20FungibleToken.bin");

Step 3: Create a function to deploy your smart contract

import { ContractCreateFlow, Client} from '@hashgraph/sdk';
* Stores the bytecode and deploys the contract to the Hedera network.
* Returns an array with the contractId and contract solidity address.
* Note: This single call handles what FileCreateTransaction(), FileAppendTransaction() and
* ContractCreateTransaction() classes do.
export const deployContract = async (client: Client, bytecode: string | Uint8Array, gasLimit: number) => {
const contractCreateFlowTxn = new ContractCreateFlow()
console.log(`- Deploying smart contract to Hedera network`)
const txnResponse = await contractCreateFlowTxn.execute(client);
const txnReceipt = await txnResponse.getReceipt(client);
const contractId = txnReceipt.contractId;
if (contractId === null ) { throw new Error("Somehow contractId is null.");}
const contractSolidityAddress = contractId.toSolidityAddress();
console.log(`- The smart contract Id is ${contractId}`);
console.log(`- The smart contract Id in Solidity format is ${contractSolidityAddress}\n`);
return [contractId, contractSolidityAddress];

Step 4: Call your function that deploys your smart contract to the Hedera network

const hederaFoundryExample = async () => {
// read the bytecode
const bytecode = fs.readFileSync("binaries/contracts_Counter_sol_Counter.bin");
// Deploy contract
const gasLimit = 1000000;
const [contractId, contractSolidityAddress] = await deployContract(client, bytecode, gasLimit);

Forge Gas Reports

Forge has functionality built in to give you gas reports of your contracts. First, configure your foundry.toml to specify which contracts should generate a gas report.
Add the below line to your foundry.toml file:
gas_reports = ["TodoList"]
In order to generate a gas report run the following command in your VSCode terminal:
forge test –gas-report
Your output will show you an estimated gas average, median, and max for each contract function and total deployment cost and size.


In this tutorial, we have learned how to configure Foundry to work with a Hedera project to test our smart contracts using the forge framework. We also learned how to generate gas reports for our smart contracts.
Happy Building! Feel free to reach out in Discord if you have any questions!

Additional Resources

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