Add first ERC721 version + Solidity test suite

solidity/src/MaybeMintERC721.sol

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+pragma solidity 0.8.24;
+
+import {ERC721} from "@openzeppelin/contracts/token/ERC721/ERC721.sol";
+import {IERC20} from "@openzeppelin/contracts/token/ERC20/IERC20.sol";
+import {Ownable} from "@openzeppelin/contracts/access/Ownable.sol";
+
+/**
+ * @title MaybeMintERC721
+ * @dev Mint ERC721 tokens for a fee in ERC20 tokens. As this simple token is intended for
+ *      demonstration of batched EVM calls on Flow EVM using a single Cadence transaction, the
+ *      minting process is random and has some chance of failure.
+ */
+contract MaybeMintERC721 is ERC721, Ownable {
+    IERC20 public denomination;
+    uint256 public mintCost;
+    address public beneficiary;
+    uint256 public totalSupply;
+
+    constructor(string memory _name, string memory _symbol, address _erc20, uint256 _mintCost, address _beneficiary)
+        ERC721(_name, _symbol)
+        Ownable(msg.sender)
+    {
+        denomination = IERC20(_erc20);
+        mintCost = _mintCost;
+        beneficiary = _beneficiary;
+        totalSupply = 0;
+    }
+
+    /**
+     * @dev Mint a new ERC721 token to the caller with some chance of failure. This is for
+     *      demonstration purposes, intended to showcase how a single Cadence transaction can batch
+     *      multiple EVM calls and condition final execution based on the result of any individual
+     *      EVM call.
+     *
+     *      NOTE: This contract address must be approved to transfer mintCost amount from the caller
+     *      to the beneficiary before minting the ERC721 to pay for mint
+     */
+    function mint() external {
+        // TODO: Get a random number to determine if the mint is successful
+        // TODO: Set token URI
+        totalSupply++; // increment the total supply
+        denomination.transferFrom(msg.sender, beneficiary, mintCost); // take payment for mint
+        _mint(msg.sender, totalSupply); // mint the token, assigning the next tokenId
+    }
+}

solidity/src/test/ExampleERC20.sol

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+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.17;
+
+import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
+import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Burnable.sol";
+import "@openzeppelin/contracts/access/Ownable.sol";
+import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Permit.sol";
+
+contract ExampleERC20 is ERC20, ERC20Burnable, Ownable, ERC20Permit {
+    constructor() ERC20("NAME", "SYMBOL") Ownable(msg.sender) ERC20Permit("NAME") {}
+
+    function mint(address to, uint256 amount) public onlyOwner {
+        _mint(to, amount);
+    }
+}

solidity/test/MaybeMintERC721.t.sol

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+pragma solidity 0.8.24;
+
+import {Test} from "forge-std/Test.sol";
+import {ERC721} from "@openzeppelin/contracts/token/ERC721/ERC721.sol";
+import {ERC20} from "@openzeppelin/contracts/token/ERC20/ERC20.sol";
+import {Ownable} from "@openzeppelin/contracts/access/Ownable.sol";
+import {MaybeMintERC721} from "../src/MaybeMintERC721.sol";
+import {ExampleERC20} from "../src/test/ExampleERC20.sol";
+
+contract MaybeMintERC721Test is Test {
+    // Contracts
+    MaybeMintERC721 private erc721;
+    ExampleERC20 private erc20;
+
+    // MaybeMintERC721 parameters
+    address payable beneficiary = payable(address(100));
+    uint256 internal mintCost = 1 ether;
+    string internal name = "Maybe Mint ERC721 Test";
+    string internal symbol = "MAYBE";
+
+    // Test values
+    address payable internal user = payable(address(101));
+
+    function setUp() public virtual {
+        vm.deal(user, 10 ether);
+
+        erc20 = new ExampleERC20();
+        erc721 = new MaybeMintERC721(name, symbol, address(erc20), mintCost, beneficiary);
+    }
+
+    function test_mint() public {
+        erc20.mint(user, mintCost); // mint ERC20 to user
+
+        vm.prank(user);
+        erc20.approve(address(erc721), mintCost); // approve the ERC20 to be spent by MaybeMintERC721
+
+        vm.prank(user);
+        erc721.mint(); // mint ERC721 to user
+
+        assertEq(erc721.ownerOf(1), user); // user should own the ERC721 token
+    }
+}