add test

test/ units/ERC721.t.sol

@@ -0,0 +1,25 @@
+//SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0;
+
+import {Test} from "forge-std/Test.sol";
+import {ERC721} from "src/ERC721.sol";
+
+contract ERC721Test is Test {
+
+    ERC721 public erc721;
+
+    function setUp() public override {
+        erc721 = new ERC721();
+    }
+
+    function testERC721() public {
+        // Test ERC721
+        // Test supportsInterface
+        assertTrue(erc721.supportsInterface(type(IERC721).interfaceId));
+        assertTrue(erc721.supportsInterface(type(IERC165).interfaceId));
+        // Test balanceOf
+        assertEquals(erc721.balanceOf(address(this)), 0);
+        // Test ownerOf
+        assertEquals(erc721.ownerOf(0), address(0));
+    }
+}