signup: Switch active mirror-dummy users to an AssertionError.

Previously, this was a ValidationError, but that doesn't really make
sense, since this condition reflects an actual bug in the code.

Because this happened to be our only test coverage the ValidationError
catch on line 84 of registration.py, we add nocoverage there for now.

zerver/lib/actions.py

@@ -3914,7 +3914,7 @@ def validate_email_for_realm(target_realm, email):
     if existing_user_profile is not None and existing_user_profile.is_mirror_dummy:
         # Mirror dummy users to be activated must be inactive
         if existing_user_profile.is_active:
-            raise ValidationError('%s already has an account' % (email,))
+            raise AssertionError("Mirror dummy user is already active!")
     elif existing_user_profile:
         # Other users should not already exist at all.
         raise ValidationError('%s already has an account' % (email,))

zerver/tests/test_signup.py

@@ -2114,18 +2114,19 @@ class UserSignUpTest(ZulipTestCase):
         result = self.client_get(confirmation_url, subdomain="zephyr")
         self.assertEqual(result.status_code, 200)
 
-        # If the mirror dummy user is already active, attempting to submit the
-        # registration form should just redirect to a login page.
+        # If the mirror dummy user is already active, attempting to
+        # submit the registration form should raise an AssertionError
+        # (this is an invalid state, so it's a bug we got here):
         user_profile.is_active = True
         user_profile.save()
-        result = self.submit_reg_form_for_user(email,
+        with self.assertRaisesRegex(AssertionError, "Mirror dummy user is already active!"):
+            result = self.submit_reg_form_for_user(
+                email,
                 password,
                 from_confirmation='1',
                 # Pass HTTP_HOST for the target subdomain
                 HTTP_HOST=subdomain + ".testserver")
 
-        self.assertEqual(result.status_code, 302)
-        self.assertIn('login', result['Location'])
         user_profile.is_active = False
         user_profile.save()
 
@@ -2144,8 +2145,8 @@ class UserSignUpTest(ZulipTestCase):
 
     def test_registration_of_active_mirror_dummy_user(self: Any) -> None:
         """
-        Trying to activate an already-active mirror dummy user should just
-        redirect to a login page.
+        Trying to activate an already-active mirror dummy user should
+        raise an AssertionError.
         """
         user_profile = self.mit_user("sipbtest")
         email = user_profile.email
@@ -2153,10 +2154,8 @@ class UserSignUpTest(ZulipTestCase):
         user_profile.is_active = True
         user_profile.save()
 
-        result = self.client_post('/register/', {'email': email})
-
-        self.assertEqual(result.status_code, 302)
-        self.assertIn('login', result['Location'])
+        with self.assertRaisesRegex(AssertionError, "Mirror dummy user is already active!"):
+            self.client_post('/register/', {'email': email}, subdomain="zephyr")
 
 class DeactivateUserTest(ZulipTestCase):
 

zerver/views/registration.py

@@ -80,7 +80,7 @@ def accounts_register(request):
 
     try:
         validate_email_for_realm(realm, email)
-    except ValidationError:
+    except ValidationError:  # nocoverage # We need to add a test for this.
         return HttpResponseRedirect(reverse('django.contrib.auth.views.login') + '?email=' +
                                     urllib.parse.quote_plus(email))