In my article Smart contracts for the impatient I documented how to deploy a contract using Mist to the testnet Rinkeby.

While it is a good example for demonstration purposes, we’ll probably go crazy if we try to deploy a Ðapp or contract doing everything manually.

What if we could develop for Ethereum, just as if we were building yet another JavaScript application. What if we could:

Automatically test our contracts or Ðapps before deploying to a real network?

Deploy contracts with a simple command?

Write contracts in a modular way?

Interact with our contracts through a CLI?

Have automatic linting?

Truffle

Truffle is a development framework for Ethereum, it not only offers all the things listed above but even more!

From their README, they describe themselves as:

YOUR ETHEREUM SWISS ARMY KNIFE

For people familiar with JavaScript and Ember.js, we could say Truffle is the ember-cli for Ethereum.

The goal of this article is to teach people how to:

Install Truffle.

Use the Ethereum RPC client for testing and development.

Familiarize with the basic concepts in Truffle.

Write the “Hello World” contract including tests.

Deploy the contract to Rinkeby.

Basic familiarity with JavaScript and Node.js is required, and we assume people is using macOS and Node.js higher or equal to 7.6.

Installing Truffle

We can install Truffle using npm , from their guide:

npm install -g truffle

After running the command above, we should we able to do the following and see some kind of output:

$ truffle Truffle v3.2.5 - a development framework for Ethereum Usage: truffle <command> [options] Commands: init Initialize new Ethereum project with example contracts and tests compile Compile contract source files migrate Run migrations to deploy contracts deploy (alias for migrate) build Execute build pipeline (if configu

Testrpc

In theory we could use Rinkeby for development, but relying on a real blockchain for development is not very efficient. We don’t want to use our test Ether or wait for transactions to complete. Also, since we don’t have control of such network, it would be very hard for us to write test in a deterministic way.

The Ethereum JavaScript community has an Ethereum RPC client for testing and development, which allow us to mock our interactions with a real network.

The name of the project is testrpc:

testrpc is a Node.js based Ethereum client for testing and development. It uses ethereumjs to simulate full client behavior and make developing Ethereum applications much faster. It also includes all popular RPC functions and features (like events) and can be run deterministically to make development a breeze.

Since it’s published as an npm package, we can install it with the following command:

npm install -g ethereumjs-testrpc

Once testrpc is installed, we can start the client by running testrpc .

$ testrpc EthereumJS TestRPC v3.0.5 Available Accounts ================== (0) 0x05dd2f0e2c917d2f83770403359cab4b1645ab9c (1) 0xaefcaeeda04808db06abf62a29cfccc2892c48e3 (2) 0xbd3d2750e62063ace2f6bc7157e4d8a81c36093b (3) 0x91c86d236cc301756effae9db74ce8cb3a3c6a1e (4) 0x1fed08900dd0420235dc9bb812483299f74200e2 (5) 0xe42e9f89b2d96ab6dd4711da4ebee4d0f792fb1b (6) 0x4166f9a27a7303f3c820d85c0f1641315cfa0474 (7) 0x51691ae53211fa46c4b1b99d42255e02905f400f (8) 0x8dbfdced435891e24e0fa4c54dde78ea843f94e2 (9) 0xcbd1865983eabac38e3816cdc257bb4fcc65f9d0 Private Keys ================== (0) 8f2dbfaab1307655f2e5751e9f4ff997b5ce312b4b50b14cbd26cb71f89b5b0e (1) 2c8c794d7f82ccccdad471aa9d82f59c13396ec266c5cbc227bfe5a7df04f94f (2) 55d116cef11e807098f5dac5120b843b1535235241a044f7a0a50cefbd2e3b8e (3) 63ef474c8f686774d38f420af459ad32978757dc40c9c28fbdfc46aa161f5362 (4) 5719fa65b2f360b778dff07ef7daad555cfee0b80988c8a5480a9241c63a5898 (5) 0b73f66a37fb65dd6410c55ae0293899bf72ccc98b18766b5bc107bfac40f0d7 (6) 46d745be848383573207615b213abde5c70ec078d2bf087de9de4e1b577368ee (7) d3b4a15fb0f13a77c34edd5e630bae7c4faf49eba81573a274fa2abe14db3759 (8) fdfd64d0167d716bc743bdd1ddb45bb82a6d01fa6db02cebbb8d568dd57b91d3 (9) 1ae6c6c0cbf4d380adef1a718bf2a2cd62a89212f60cf672a77aaeeb543c1a80 HD Wallet ================== Mnemonic: audit can stock squeeze equip aerobic abuse access fringe grocery stone novel Base HD Path: m/44'/60'/0'/0/{account_index} Listening on localhost:8545

As a quick test, we can start Mist using this client instead of geth and then we should see all the wallets listed above with some Ether.

/Applications/Mist.app/Contents/MacOS/Mist --rpc http://localhost:8545

Keep testrpc running and now let’s start using Truffle.

Starting a project

To create a new project do the following:

$ mkdir hello-world $ cd hello-world $ truffle init

After creating the project, we’ll see a basic skeleton app, we can test that everything is working by running the default test:

$ truffle test Using network 'development'. Compiling ./contracts/ConvertLib.sol... Compiling ./contracts/MetaCoin.sol... Compiling ./test/TestMetacoin.sol... Compiling truffle/Assert.sol... Compiling truffle/DeployedAddresses.sol... TestMetacoin ✓ testInitialBalanceUsingDeployedContract (63ms) ✓ testInitialBalanceWithNewMetaCoin (60ms) Contract: MetaCoin ✓ should put 10000 MetaCoin in the first account (63ms) ✓ should call a function that depends on a linked library (79ms) ✓ should send coin correctly (173ms) 5 passing (840ms)

The command truffle init uses the following repo as default blueprint https://github.com/trufflesuite/truffle-init-default, it includes an example contract and tests.

Since we are going to be writing our own contract and tests, we are going to remove some of the defaults:

rm contracts/ConvertLib.sol contracts/MetaCoin.sol rm test/TestMetacoin.sol test/metacoin.js rm migrations/2_deploy_contracts.js

Creating contracts with Truffle and testing

To create a new contract, run the command truffle create . It requires the type of item we want to create and the name.

truffle create contract HelloWorld

The name must be CamelCased . After running the command, the file will be under contracts/HelloWorld.sol with the following content:

pragma solidity ^ 0.4 . 4 ; contract HelloWorld { function HelloWorld () { // constructor } }

Next, add the code for the hello world contract.

pragma solidity ^ 0.4 . 4 ; contract HelloWorld { //Begin: state variables address private creator ; address private lastCaller ; string private message ; uint private totalGas ; //End: state variables //Begin: constructor function HelloWorld () { /* We can use the special variable `tx` which gives us information about the current transaction. `tx.origin` returns the sender of the transaction. `tx.gasprice` returns how much we pay for the transaction */ creator = tx . origin ; totalGas = tx . gasprice ; message = 'hello world' ; } //End: constructor //Begin: getters function getMessage () constant returns ( string ) { return message ; } function getLastCaller () constant returns ( address ) { return lastCaller ; } function getCreator () constant returns ( address ) { return creator ; } function getTotalGas () constant returns ( uint ) { return totalGas ; } //End: getters //Being: setters function setMessage ( string newMessage ) { message = newMessage ; lastCaller = tx . origin ; totalGas += tx . gasprice ; } //End: setters }

Migration

Once we have the code for the contract, we need to find a way to deploy it into the blockchain. Truffle has a primitive called migration, which can be used to compose and deploy contracts.

Create a migration called deploy_hello_world :

$ truffle create migration deploy_hello_world $ git st On branch master Untracked files: (use "git add <file>..." to include in what will be committed) migrations/1499575148_deploy_hello_world.js

Above we can see that a new file got created (if you get a different result, it means the following PR has not been merged yet https://github.com/trufflesuite/truffle-core/pull/13, rename it so it look similar to the one above).

Next, update the code for the contract to deploy our HelloWorld example, to do so we’ll require the contract and then use the deployer:

// We use artifacts.require to tell Truffle which artifacts we'll be // interacting with. // In the example below, we are requiring the contract HelloWorld // which returns an abstraction that we can use for the deployment. const HelloWorld = artifacts . require ( 'HelloWorld' ) module . exports = function ( deployer ) { deployer . deploy ( HelloWorld ) } // Read more about artifacts here http://truffleframework.com/docs/getting_started/migrations#artifacts-require-

We should be able to deploy the contract to the test blockchain running truffle migrate --reset :

$ truffle migrate --reset Compiling ./contracts/HelloWorld.sol... Compiling ./contracts/Migrations.sol... Writing artifacts to ./build/contracts Using network 'development' . Running migration: 1_initial_migration.js Deploying Migrations... Migrations: 0x665311133c3f2ca24c633da656ded48619fb3239 Saving successful migration to network... Saving artifacts... Running migration: 1499575148_deploy_hello_world.js Deploying HelloWorld... HelloWorld: 0xba06f7905d9c4584be914365ae1ce44688e50504 Saving successful migration to network... Saving artifacts...

If we look at the log from testrpc we’ll see a register of the transactions:

eth_sendTransaction Transaction: 0x11316dc23e638f8d9aaae06fd0751a209f94ed2dd1c42307cf25c6c01198f0df Contract created: 0xba06f7905d9c4584be914365ae1ce44688e50504 Gas usage: 0x05a8a4 Block Number: 0x07 Block Time: Sat Jul 08 2017 22:21:52 GMT-0700 ( PDT ) eth_sendTransaction Transaction: 0x3b0c127d8a8ffe1465091a4208204b97016991f4396d19e40edcbd8323988a7a Gas usage: 0x696e Block Number: 0x08 Block Time: Sat Jul 08 2017 22:21:53 GMT-0700 ( PDT )

We have successfully deployed a contract using Truffle to testrpc but we haven’t written any test yet. That’s what we’ll do next.

Testing

Truffle has built-in support for testing. We’ll write some test for the methods defined in our contract.

To create the test we need to run the command truffle create test HelloWorld and then put the following content in test/hello_world.js :

const HelloWorld = artifacts.require('HelloWorld') contract('HelloWorld', function(accounts) { it('sets the first account as the contract creator', async function() { // This give a truffle abstraction which allow us to interact with our contracts. const contract = await HelloWorld.deployed() // Once we have the "contract" we can make calls or transations and then assert. // The following is making a call to get the creator. const creator = await contract.getCreator() assert.equal(creator, accounts[0], 'main account is the creator') }) it('has hello world as initial message ', async function() { const contract = await HelloWorld.deployed() const message = await contract.getMessage() assert.equal(message, 'hello world', 'message is hello world') }) it('changes the message via setMessage', async function() { const contract = await HelloWorld.deployed() // Execute a transaction and change the state of the contract. await contract.setMessage('hola mundo') // Get the new state. const message = await contract.getMessage() assert.equal(message, 'hola mundo', 'message is hola mundo') }) })

Once we have the test file setup, we can run our tests with the command truffle test .

$ truffle test Compiling ./contracts/HelloWorld.sol... Compiling ./contracts/Migrations.sol... Contract: HelloWorld ✓ sets the first account as the contract creator ( 47ms ) ✓ has hello world as initial message ( 44ms ) ✓ changes the message via setMessage ( 80ms ) 3 passing ( 197ms )

Wrapping up

In this article, we covered how to create, test and deploy a contract using Truffle and testrpc. In Deploying Truffle contracts to Rinkeby, we’ll see how to add networks and deploy to Rinkeby. Follow me on twitter (@abuiles) or subscribe to my feed to get updates on my post.

You can find the code and steps for this article in GitHub https://github.com/abuiles/Writing-Smart-Contracts-With-Truffle.

Finally, we talked superficially about Truffle’s contracts, migrations and tests. To learn more about it check their website.