Exercise 1

Table of Contents:

• Exercise 1
  • Targeted Contract
  • Testing a Token Balance
    • Goals
  • Solution

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Targeted Contract

We will test the following contract token.sol:

pragma solidity ^0.8.0;

contract Ownable {
    address public owner = msg.sender;

    modifier onlyOwner() {
        require(msg.sender == owner, "Ownable: Caller is not the owner.");
        _;
    }
}

contract Pausable is Ownable {
    bool private _paused;

    function paused() public view returns (bool) {
        return _paused;
    }

    function pause() public onlyOwner {
        _paused = true;
    }

    function resume() public onlyOwner {
        _paused = false;
    }

    modifier whenNotPaused() {
        require(!_paused, "Pausable: Contract is paused.");
        _;
    }
}

contract Token is Ownable, Pausable {
    mapping(address => uint256) public balances;

    function transfer(address to, uint256 value) public whenNotPaused {
        // unchecked to save gas
        unchecked {
            balances[msg.sender] -= value;
            balances[to] += value;
        }
    }
}

Testing a Token Balance

Goals

• Add a property to check that the address echidna cannot have more than an initial balance of 10,000.
• After Echidna finds the bug, fix the issue, and re-check your property with Echidna.

The skeleton for this exercise is (template.sol):

pragma solidity ^0.8.0;

import "./token.sol";

/// @dev Run the template with
///      ```
///      solc-select use 0.8.0
///      echidna program-analysis/echidna/exercises/exercise1/template.sol
///      ```
contract TestToken is Token {
    address echidna = tx.origin;

    constructor() {
        balances[echidna] = 10_000;
    }

    function echidna_test_balance() public view returns (bool) {
        // TODO: add the property
    }
}

Solution

This solution can be found in solution.sol.