Create and Test a Solidity Smart Contract with a Public Variable

Instructor: [0:00] It's time to start writing Solidity. First, let's create a file for the Smart Contract. Name it as tipjar.soul. This is a Solidity file. The first thing you need to declare is the SPDX license identifier, and then choose any license. I chose GPL-3.. [0:25] Then, let's set the Solidity version using the pragma keyboard. Import a utility contract from Hardhat named console.soul. This contract allows you to print to the standard output using console.log, same as JavaScript.

[0:47] Let's create the contract by writing the contract keyword and the name of the contract. You'll notice that this is very similar to a class. Next, you'll create a public variable as integer named totalTips.

[1:06] Then a fundamental function, which is the constructor. This is an object-oriented programming language. You have constructors and the contract is like the class. Let's write the constructor, which will not accept any arguments. The only thing this constructor will do is console log that this is a smart contract.

[1:33] Let's write a little test for this. Testing smart contracts is one of the most important things you can do since the nature of blockchain is immutable, meaning that the smart contract after being deployed cannot be changed. Let's test this. Let's create a file under the test folder named tipjar.js.

[1:59] Let's require the expect library from Chai and the ethers library from Hardhat. This library will help you to interact with the smart contract. Let's describe this as the tip jar contract and write the first scenario for that.

[2:19] You will store the contract variable globally and then write the description as follows, should deploy the contract and return zero as total tips. This is an asynchronous function. The first step is to create a contract factory. This is done by using the Ethers ContractFactory function where you just pass the name of the contract that you want to deploy. In this case, tipjar is the name.

[2:50] Then, utilizing the ContractFactory, you create a contract instance, so await ContractFactory.deploy, and then we'll wait for the contract to be deployed. Now, the contract is deployed. You can expect these asynchronous functions.

[3:07] Write contract.totalTips to be equal to zero. This is what you want. If you're wondering where totalTips came from, you created a public variable earlier. Solidity will create a public getter to every public variable you make. This means it will create a public function named the same as your public variable.

[3:35] This function will return the value of that variable. In this case, it will be an unsigned integer. Now, it's time to run this test. Let's see what you have.

[3:48] Open your terminal. Be sure to cd into the tipjar folder, where the project is, and let's run hardhat test. As you can see, this fails because of some weirdness with how ES modules and CommonJS work together. What you need to do is to rename the Hardhat configuration file to be a CommonJS file.

[4:16] Then create some npm scripts inside your package.json file. To run Hardhat with this new configuration, let's make the first script to use it with the new configuration file. Then let's create one script to compile the contracts using hardhat compile. You'll do the same thing for running the test.

[4:43] Finally, a command that you'll use in the following lessons, hardhat deploy. This will just run Hardhat with a script named deploy to the local network. With this in place, it's time to run the test again.

[5:01] In your terminal run npm run hardhat test. The test will start running, compile the smart contract for you, and then check if it's passing or not. You have a green. Your smart contract is running flawlessly.

[5:18] For this lesson, you created your first contract. You made a public variable and a constructor, and you wrote your first JavaScript test using Hardhat as the development environment and ethers ES.