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Library for writing and testing smart contracts.
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Ethereum Waffle

Library for writing and testing smart contracts.

Sweeter, simpler and faster than Truffle.



  • Simpler: Minimalistic, few dependencies.
  • Sweeter: Nice syntax, easy to extend.
  • Faster: Strong focus on the speed of test execution.


  • Sweet set of chai matchers, e.g.:
    • expect(...)'Error message')
    • expect(...).to.emit(contract, 'EventName).withArgs(...))
  • Importing contracts from npm modules working out of the box, e.g.:
    • import "openzeppelin-solidity/contracts/token/ERC20/ERC20.sol";
  • Fixtures that help write fast and maintainable test suites, e.g.:
    • const {token} = await loadFixture(standardTokenWithBalance);
  • Customizable compilation options with native solc, dockerized solc and any version of solc-js loaded remotely at compiled time
  • Support for promise-based configuration, e.g.:
    • use native solc binary for fast compilation in CI environment
    • use solc-js based on contract versions detected (async)
  • Support for TypeScript
  • Documentation


Documentation is available here.


To get started install ethereum-waffle with yarn:

yarn add --dev ethereum-waffle

Or if you prefer using npm:

npm install --save-dev ethereum-waffle

Step by step guide

Add external dependency:

To add an external library install it using npm:

npm i openzeppelin-solidity -D

or with yarn:

yarn add openzeppelin-solidity -D

Example contract

Below is an example contract written in Solidity. Place it in contracts/BasicToken.sol file of your project:

// contracts/BasicToken.sol
pragma solidity ^0.5.1;

import "openzeppelin-solidity/contracts/token/ERC20/ERC20.sol";

// Example class - a mock class using delivering from ERC20
contract BasicToken is ERC20 {
  constructor(address initialAccount, uint256 initialBalance) public {
    super._mint(initialAccount, initialBalance);

Example test

Below is an example test written for the contract above compiled with Waffle. Place it under test/BasicToken.js file of your project:

// test/BasicToken.js
const {use, expect} = require('chai');
const {MockProvider, deployContract, solidity} = require('ethereum-waffle');
const BasicToken = require('../build/BasicToken');


describe('BasicToken', () => {
  const [wallet, walletTo] = new MockProvider().getWallets();
  let token;

  beforeEach(async () => {
    token = await deployContract(wallet, BasicTokenMock, [wallet.address, 1000]);

  it('Assigns initial balance', async () => {
    expect(await token.balanceOf(wallet.address)).to.equal(1000);

  it('Transfer adds amount to destination account', async () => {
    await token.transfer(walletTo.address, 7);
    expect(await token.balanceOf(walletTo.address)).to.equal(7);

  it('Transfer emits event', async () => {
    await expect(token.transfer(walletTo.address, 7))
      .to.emit(token, 'Transfer')
      .withArgs(wallet.address, walletTo.address, 7);

  it('Can not transfer above the amount', async () => {
    await expect(token.transfer(walletTo.address, 1007));

  it('Can not transfer from empty account', async () => {
    const tokenFromOtherWallet = token.connect(walletTo);
    await expect(tokenFromOtherWallet.transfer(wallet.address, 1));

Note: You will also need to install following dependencies with to run the example above:

yarn add mocha -D
yarn add chai -D

Or with npm:

npm i chai -D
npm i mocha -D


To compile your smart contracts run:

npx waffle

To compile using a custom configuration file run:

npx waffle config.json

Example configuration file looks like this (all fields optional):

  "sourcesPath": "./custom_contracts",
  "targetPath": "./custom_build",
  "npmPath": "./custom_node_modules"

Running tests

To run the tests run the following command:

npx mocha

Adding an npm script

For convinience, you can add the following to your package.json:

  "scripts": {
    "test": "waffle && mocha"

Now you can build and test your contracts with one command:

npm test


For detailed feature walkthrough checkout documentation.


Contributions are always welcome, no matter how large or small. Before contributing, please read the code of conduct and contribution policy.

Before you issue pull request:

Make sure all tests and linters pass. Make sure you have test coverage for any new features.

Running tests

Note: To make end-to-end test pass, you need to:

  • have Docker installed, up and running
  • have Ethereum stable docker image pulled, if not run docker pull ethereum/solc:stable
  • have native solidity 0.5.* installed

To run tests type:

yarn test

To run linter type:

yarn lint

Building documentation (requires Sphinx):

cd docs
make html




Waffle is released under the MIT License.

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