allow the socket mode receiver to be used with socket mode

src/App-basic-features.spec.ts

@@ -14,6 +14,7 @@ import {
 } from './types';
 import { ConversationStore } from './conversation-store';
 import App from './App';
+import SocketModeReceiver from './receivers/SocketModeReceiver';
 
 // Utility functions
 const noop = () => Promise.resolve(undefined);
@@ -264,7 +265,7 @@ describe('App basic features', () => {
         assert.propertyVal(error, 'code', ErrorCode.AppInitializationError);
       }
     });
-    it('should fail when both socketMode and receiver are specified', async () => {
+    it('should fail when both socketMode and a custom receiver are specified', async () => {
       // Arrange
       const fakeReceiver = new FakeReceiver();
       const MockApp = await importApp();
@@ -278,6 +279,23 @@ describe('App basic features', () => {
         assert.propertyVal(error, 'code', ErrorCode.AppInitializationError);
       }
     });
+    it('should succeed when both socketMode and SocketModeReceiver are specified', async () => {
+      // Arrange
+      const fakeBotId = 'B_FAKE_BOT_ID';
+      const fakeBotUserId = 'U_FAKE_BOT_USER_ID';
+      const overrides = mergeOverrides(
+        withNoopAppMetadata(),
+        withSuccessfulBotUserFetchingWebClient(fakeBotId, fakeBotUserId),
+      );
+      const MockApp = await importApp(overrides);
+      const socketModeReceiver = new SocketModeReceiver({ appToken: '' });
+
+      // Act
+      const app = new MockApp({ token: '', signingSecret: '', socketMode: true, receiver: socketModeReceiver });
+
+      // Assert
+      assert.instanceOf(app, MockApp);
+    });
     it('should initialize MemoryStore conversation store by default', async () => {
       // Arrange
       const fakeMemoryStore = sinon.fake();

src/App.ts

@@ -1177,10 +1177,7 @@ export default class App<AppCustomContext extends StringIndexed = StringIndexed>
   ): Receiver {
     if (receiver !== undefined) {
       // Custom receiver supplied
-      if (this.socketMode === true) {
-        // socketMode = true should result in SocketModeReceiver being used as receiver
-        // TODO: Add case for when socketMode = true and receiver = SocketModeReceiver
-        // as this should not result in an error
+      if (this.socketMode === true && !(receiver instanceof SocketModeReceiver)) {
         throw new AppInitializationError('You cannot supply a custom receiver when socketMode is set to true.');
       }
       return receiver;