test(auth, multi-tenant): add multi-tenant E2E test

this exposed most of the errors fixed in prior commits, and allows you
to see that setTenantId is working, but cannot be used against the emulator
and we have no valid tenant id in our test project so it is unknown if this
is truly working

packages/auth/e2e/auth.e2e.js

@@ -1071,4 +1071,25 @@ describe('auth()', function () {
       }
     });
   });
+
+  describe('setTenantId()', function () {
+    it('should return null if tenantId unset', function () {
+      should.not.exist(firebase.auth().tenantId);
+    });
+
+    // multi-tenant is not supported by the firebase auth emulator, and requires a valid multi-tenant tenantid
+    // After setting this, next user creation will result in internal error on emulator, or auth/invalid-tenant-id live
+    // it('should return tenantId correctly after setting', async function () {
+    //   await firebase.auth().setTenantId('testTenantId');
+    //   firebase.auth().tenantId.should.equal('testTenantId');
+    // });
+    // it('user should have tenant after setting tenantId', async function () {
+    //   await firebase.auth().setTenantId('userTestTenantId');
+    //   firebase.auth().tenantId.should.equal('userTestTenantId');
+    //   const random = Utils.randString(12, '#a');
+    //   const email = `${random}@${random}.com`;
+    //   const userCredential = await firebase.auth().createUserWithEmailAndPassword(email, random);
+    //   userCredential.user.tenantId.should.equal('userTestTenantId');
+    // });
+  });
 });