# Getting Started with Gas Profiling

          Begin by creating a smart contract named `Inventory` with the following configuration:

```solidity
// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.20;

contract Inventory {
    address public manager;
    uint256 public totalProducts;

    struct Product {
        uint256 id;
        string description;
        uint256 price;
    }

    mapping(uint256 => Product) public products;

    constructor() {
        manager = msg.sender;
    }

    function addProduct(string memory description, uint256 price) external {
        require(msg.sender == manager, "invalid manager");
        totalProducts++;
        products[totalProducts] = Product(
            totalProducts,
            description,
            price
        );
    }
}

```

          Add a test file named `Inventory.js` to evaluate the gas reporter plugin. This file should include the following content:

```javascript
const { expect } = require("chai");
const { ethers } = require("hardhat");

describe.only("Inventory tests", function () {
  let instance;
  let owner;

  before(async () => {
    const Inventory = await ethers.getContractFactory("Inventory");
    instance = await Inventory.deploy();
    await instance.waitForDeployment();

    const signers = await ethers.getSigners();
    owner = signers[0];
  });

  it("should add a product", async () => {
    const description = "Laptop";
    const price = ethers.parseEther("1.5");

    await instance.addProduct(description, price);

    expect(await instance.totalProducts()).to.equal(1);
  });

  it("should store product details correctly", async () => {
    const description = "Mouse";
    const price = ethers.parseEther("0.05");

    await instance.addProduct(description, price);
    const product = await instance.products(2);

    expect(product.id).to.equal(2);
    expect(product.description).to.equal(description);
    expect(product.price).to.equal(price);
  });

  it("should only allow manager to add products", async () => {
    const signers = await ethers.getSigners();
    const nonManager = signers[1];

    const description = "Keyboard";
    const price = ethers.parseEther("0.1");

    await expect(
      instance.connect(nonManager).addProduct(description, price)
    ).to.be.revertedWith("invalid manager");
  });

  it("should verify manager is set correctly", async () => {
    expect(await instance.manager()).to.equal(owner.address);
  });
});

```

          Run `npx hardhat test` to execute the tests. A gas usage report will be generated as shown below:

<figure><img src="https://1670530031-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FNGHmFVO7DlELOLs4PSVs%2Fuploads%2FgniH7bg0fDLs8xSLWeMV%2Fimage14.png?alt=media&#x26;token=b9c2fd28-7108-430a-821f-387c1e617fcb" alt=""><figcaption></figcaption></figure>