Update docs

test/helpers/methods.js

@@ -1,5 +1,14 @@
-const { soliditySha3 } = require('web3-utils');
+const { ethers } = require('hardhat');
+
+const selector = signature => ethers.FunctionFragment.from(signature).selector;
+
+const interfaceId = signatures =>
+  ethers.toBeHex(
+    signatures.reduce((acc, signature) => acc ^ ethers.toBigInt(selector(signature)), 0n),
+    4,
+  );
 
 module.exports = {
-  selector: signature => soliditySha3(signature).substring(0, 10),
+  selector,
+  interfaceId,
 };