fixes for ERC721 hardhat examples

Author: tuturu-tech

tests/ERC721/hardhat/contracts/CryticTest.sol

@@ -3,15 +3,40 @@ import "@crytic/properties/ERC721/internal/properties/ERC721BasicProperties.sol"
 import "./ExampleToken.sol";
 
 contract CryticERC721InternalHarness is ExampleToken, CryticERC721BasicProperties {
+    using Address for address;
+
     constructor() {
+        maxSupply = 100;
         isMintableOrBurnable = true;
+        hasMaxSupply = false;
+        safeReceiver = new MockReceiver(true);
+        unsafeReceiver = new MockReceiver(false);
     }
 
     function _customMint(uint256 amount) internal virtual {
-        mint(amount);
+        mint(msg.sender, amount);
     }
 
     function _customMaxSupply() internal virtual view returns (uint256) {
         return maxSupply;
     }
+
+        // The following functions are overrides required by Solidity.
+    function _beforeTokenTransfer(address from, address to, uint256 tokenId, uint256 batchSize)
+        internal
+        virtual
+        override(ExampleToken, CryticERC721TestBase)
+    {
+        super._beforeTokenTransfer(from, to, tokenId, batchSize);
+    }
+
+    function supportsInterface(bytes4 interfaceId)
+        public
+        view
+        virtual
+        override(ExampleToken, CryticERC721TestBase)
+        returns (bool)
+    {
+        return super.supportsInterface(interfaceId);
+    }
 }

tests/ERC721/hardhat/contracts/CryticTestExt.sol

@@ -2,12 +2,15 @@ pragma solidity ^0.8.0;
 import "./ExampleToken.sol";
 import {IERC721Internal} from "@crytic/properties/ERC721/util/IERC721Internal.sol";
 import {CryticERC721ExternalBasicProperties} from "@crytic/properties/ERC721/external/properties/ERC721xternalBasicProperties.sol";
+import {MockReceiver} from "properties/ERC721/external/util/MockReceiver.sol";
 
 contract CryticERC721ExternalHarness is CryticERC721ExternalBasicProperties {
 
     constructor() {
         // Deploy ERC721
         token = IERC721Internal(address(new ERC721Mock()));
+        mockSafeReceiver = new MockReceiver(true);
+        mockUnsafeReceiver = new MockReceiver(false);
     }
 
 }

tests/ERC721/hardhat/contracts/ExampleToken.sol

@@ -5,16 +5,21 @@ import "@openzeppelin/contracts/token/ERC721/extensions/ERC721Burnable.sol";
 import "@openzeppelin/contracts/token/ERC721/extensions/ERC721Enumerable.sol";
 
 contract ExampleToken is ERC721, ERC721Enumerable, ERC721Burnable {
+    
+    uint256 public counter;
     constructor() ERC721("Example token", "EXT") {}
 
-    function mint(address to, uint256 tokenId) public virtual {
-        _mint(to, tokenId);
+    function mint(address to, uint256 amount) public {
+        for (uint256 i; i < amount; i++) {
+            _mint(to, counter++);
+        }
     }
 
     // Overrides
 
     function _beforeTokenTransfer(address from, address to, uint256 tokenId, uint256 batchSize)
         internal
+        virtual
         override(ERC721, ERC721Enumerable)
     {
         super._beforeTokenTransfer(from, to, tokenId, batchSize);
@@ -23,6 +28,7 @@ contract ExampleToken is ERC721, ERC721Enumerable, ERC721Burnable {
     function supportsInterface(bytes4 interfaceId)
         public
         view
+        virtual
         override(ERC721, ERC721Enumerable)
         returns (bool)
     {