Address comments

Author: mansisampat

packages/auth/src/core/auth/firebase_internal.test.ts

@@ -328,7 +328,7 @@ describe('core/auth/firebase_internal - Regional Firebase Auth', () => {
   });
 
   context('getUid', () => {
-    it('returns null if currentUser is undefined', () => {
+    it('throws an error if regionalAuth is initialized', () => {
       expect(() => regionalAuthInternal.getUid()).to.throw(
         FirebaseError,
         'auth/operation-not-allowed'

packages/auth/src/core/auth/firebase_internal.ts

@@ -36,6 +36,7 @@ export class AuthInterop implements FirebaseAuthInternal {
 
   getUid(): string | null {
     this.assertAuthConfigured();
+    // getUid() is not available for regional Auth. Returns `OPERATION_NOT_ALLOWED` exception for RegionalAuth.
     this.assertRegionalAuthConfigured();
     return this.auth.currentUser?.uid || null;
   }