Update docs

test/metatx/ERC2771Context.test.js

@@ -12,6 +12,8 @@ const ContextMockCaller = artifacts.require('ContextMockCaller');
 const { shouldBehaveLikeRegularContext } = require('../utils/Context.behavior');
 
 contract('ERC2771Context', function (accounts) {
+  const [, anotherAccount] = accounts;
+
   beforeEach(async function () {
     this.forwarder = await MinimalForwarder.new();
     this.recipient = await ERC2771ContextMock.new(this.forwarder.address);
@@ -73,6 +75,15 @@ contract('ERC2771Context', function (accounts) {
         const { tx } = await this.forwarder.execute(req, sign);
         await expectEvent.inTransaction(tx, ERC2771ContextMock, 'Sender', { sender: this.sender });
       });
+
+      it('returns the original sender when calldata length is less than 20 bytes (address length)', async function () {
+        // The forwarder doesn't produce calls with calldata length less than 20 bytes
+        const recipient = await ERC2771ContextMock.new(anotherAccount);
+
+        const { receipt } = await recipient.msgSender({ from: anotherAccount });
+
+        await expectEvent(receipt, 'Sender', { sender: anotherAccount });
+      });
     });
 
     describe('msgData', function () {