add 165 to 721 (#972)

* make _tokenId indexed in Transfer and Approval events

via: https://github.com/ethereum/EIPs/pull/1124/files

* fix: make name() and symbol() external instead of public

* feat: implement ERC721's ERC165

* feat: erc165 tests

* fix: don't use chai-as-promised in direct await

* fix: reorganize to /introspection

* feat: abstract all erc165 tests to a behavior

* feat: disallow registering 0xffffffff

test/introspection/SupportsInterface.behavior.js

@@ -0,0 +1,54 @@
+import makeInterfaceId from '../helpers/makeInterfaceId';
+
+const INTERFACE_IDS = {
+  ERC165: makeInterfaceId([
+    'supportsInterface(bytes4)',
+  ]),
+  ERC721: makeInterfaceId([
+    'balanceOf(address)',
+    'ownerOf(uint256)',
+    'approve(address,uint256)',
+    'getApproved(uint256)',
+    'setApprovalForAll(address,bool)',
+    'isApprovedForAll(address,address)',
+    'transferFrom(address,address,uint256)',
+    'safeTransferFrom(address,address,uint256)',
+    'safeTransferFrom(address,address,uint256,bytes)',
+  ]),
+  ERC721Enumerable: makeInterfaceId([
+    'totalSupply()',
+    'tokenOfOwnerByIndex(address,uint256)',
+    'tokenByIndex(uint256)',
+  ]),
+  ERC721Metadata: makeInterfaceId([
+    'name()',
+    'symbol()',
+    'tokenURI(uint256)',
+  ]),
+  ERC721Exists: makeInterfaceId([
+    'exists(uint256)',
+  ]),
+};
+
+export default function (interfaces = []) {
+  describe('ERC165\'s supportsInterface(bytes4)', function () {
+    beforeEach(function () {
+      this.thing = this.mock || this.token;
+    });
+
+    for (let k of interfaces) {
+      const interfaceId = INTERFACE_IDS[k];
+      describe(k, function () {
+        it('should use less than 30k gas', async function () {
+          const gasEstimate = await this.thing.supportsInterface.estimateGas(interfaceId);
+          gasEstimate.should.be.lte(30000);
+        });
+
+        it('is supported', async function () {
+          const isSupported = await this.thing.supportsInterface(interfaceId);
+          isSupported.should.eq(true);
+        });
+      });
+    }
+  });
+}