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Unit Testing Smart Contracts

Lesson Objectives

By the end of this lesson, you will be able to:

  • Use Truffle IDE for unit testing your smart contracts.
  • Write test cases for unit testing of your smart contracts to make sure your code works correctly before deploying it onto a blockchain network.


In the previous lessons, we outlined how to write, compile and deploy smart contract written in Solidity programming language for use on the BNB Smart Chain network using the different IDEs. In this lesson, we perform unit testing of our smart contract to make sure that its works perfectly and as desired before deploying it onto blockchain network.


In this hands-on guide, readers are encourged to perform these tasks along for a better understanding. Before starting off with the practical demo, it is necessary to make sure you have the following software requisites installed. For this tutorial, we will be using Truffle IDE for unit testing our smart contracts.


  • node v16.13.0
  • npm v8.1.0
  • Truffle v5.5.19 (core: 5.5.19)
  • Solidity - ^0.8.0 (solc-js)
  • Web3.js v1.5.3
  • MetaMask Wallet (Latest Version)


We will test out our Solidity smart contracts behaviour with unit testing with Truffle which uses Chai and Mocha frameworks. In web development lifecycle, unit testing is needed to do to ensure the code is working the way as it is expected.

In order to be able to complete this demo, make sure you have followed the tutorial Hello World Smart Contract for writing the HelloWorld smart contract using the Truffle IDE and the lesson on Compiling Smart Contracts for successfully compiled the HelloWorld smart contract.

Test Script

The firt step is to create a file in the test folder that will contain the test script. In the test folder create a new file hello_world.js

In the hello_world.js file residing in the test folder, copy and paste the code given below.

var helloworld = artifacts.require('../contracts/bsc/HelloWorld');

contract('HelloWorld', function(accounts) {
  let instance;
  before(async () => {
    instance = await helloworld.deployed();
  //Test to check if the default value is set to "hello, world"
  it('Default message should be hello, world',async () => {
    let message = await{from: accounts[0]});           
    assert.equal(message, "Hello, World","Incorrect Default Value");

  //Test to check if the setName is working or not
  it('Should save name',async () => {
    let result = await instance.setName.sendTransaction('BNB Chain',{from: accounts[0]}); 
    let message = await{from: accounts[0]});           
    assert.equal(message, "Hello, BNB Chain","Value Could not be Set");        

  //Test to check if error is thrown on empty name field
  it('Should throw error on empty name',async () => {
      let result = await instance.setName.sendTransaction('',{from: accounts[0]});,false,"The function should throw error");  
        assert.include(String(err),'revert','throws different error');

Explanation of the test script

  • In the beginning of the code, we tell Truffle which contracts we'd like to interact with via the artifacts.require() method. In our case, the smart contract is stored in the ../contracts/bsc/HelloWorld.
  • Next, the smart contract is deployed on the local network, using Ganache.
  • The first test performed is to check that the default value stored in the greet variable is World. If not, an message Incorrect Default Value is displayed.
  • The second test performed is to check that the setName function works properly or not. If not, an message Value Could not be Set is displayed.
  • The third test ensures that the greet variable is not set to empty value.

Running the Test Scripts

  • Open a terminal and move into the root directory of the project. Run the ganache-cli using the command ganache-cli.
  • Make sure that the terminal is not closed, i.e., ganache-cli is running in the background. This is important because testing is done on the local network.


  • From the root directory of the project, in a new terminal, run the command truffle test --config=truffle-config-bsc.js to run the tests.



In this tutorial, we covered unit testing of smart contracts using the Truffle IDE that uses Chai and Mocha frameworks for the purpose of unit testing. In order to be able to successfully complete this demo, make sure you have a truffle project created with HelloWorld smart contract as specified in the Using Truffle lesson.

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