• Initialise contract

forge init --template <https://github.com/foundry-rs/forge-template> stake

• Create a buggy StakingContract.sol

// SPDX-License-Identifier: Unlicense
pragma solidity ^0.8.13;

contract StakingContract { 
    uint256 public totalStaked;
    mapping(address => uint256) public stakedBalances;

    function stake(uint256 amount) public payable {
        require(amount > 0, "Amount must be greater than 0");
        require(msg.value == amount, "Amount must be equal to msg.value");
        totalStaked += amount;
        stakedBalances[msg.sender] += amount;
    }

    function unstake(uint256 amount) public payable {
        require(amount <= stakedBalances[msg.sender], "Not enough balance");
        totalStaked -= amount / 2;
        stakedBalances[msg.sender] -= amount / 2;
        payable(msg.sender).transfer(amount / 2);
    }
}

• Write tests for it (test the buggy implementation)

// SPDX-License-Identifier: Unlicense
pragma solidity ^0.8.13;

import "forge-std/Test.sol";

import "src/StakingContract.sol";

contract StakingTestContract is Test {
    StakingContract c;

    function setUp() public {
        c = new StakingContract();
    }

    function testStake() public {
        uint value = 10 ether;
        c.stake{value: value}(value);
        assert(c.totalStaked() == value);
    }

    function testUnStake() public {
        uint value = 10 ether;
        c.stake{value: value}(value);
        c.unstake(value);
        assert(c.totalStaked() == value / 2);
    }
}

• Alt Test for a different address

// SPDX-License-Identifier: Unlicense
pragma solidity ^0.8.13;

import "forge-std/Test.sol";

import "src/StakingContract.sol";

contract StakingTestContract is Test {
    StakingContract c;

    function setUp() public {
        c = new StakingContract();
    }

    function testStake() public {
        uint value = 10 ether;
        vm.deal(0x587EFaEe4f308aB2795ca35A27Dff8c1dfAF9e3f, value);
        vm.prank(0x587EFaEe4f308aB2795ca35A27Dff8c1dfAF9e3f);
        c.stake{value: value}(value);
        assert(c.totalStaked() == value);
    }

    function testUnStake() public {
        uint value = 11 ether;
        vm.deal(0x587EFaEe4f308aB2795ca35A27Dff8c1dfAF9e3f, value);
        vm.startPrank(0x587EFaEe4f308aB2795ca35A27Dff8c1dfAF9e3f);
        assert(address(0x587EFaEe4f308aB2795ca35A27Dff8c1dfAF9e3f).balance == value);
        c.stake{value: value}(value);
        c.unstake(value);
        assert(c.totalStaked() == value / 2);
    }
}