diff --git a/authens/tests/test_backend.py b/authens/tests/test_backend.py
index 6c77c6d..486db62 100644
--- a/authens/tests/test_backend.py
+++ b/authens/tests/test_backend.py
@@ -4,7 +4,7 @@ from django.contrib.auth import authenticate, get_user_model
 from django.test import TestCase
 
 from authens.backends import ENSCASBackend
-from authens.models import CASAccount
+from authens.models import CASAccount, OldCASAccount
 from authens.tests.cas_utils import FakeCASClient
 
 UserModel = get_user_model()
@@ -94,8 +94,31 @@ class TestCASBackend(TestCase):
         # Log the new 'johndoe' in.
         new_user = authenticate(None, ticket="dummy ticket")
         new_clipper = new_user.cas_account
-        # Check that it gets a fresh user and a fresh clipper account.
+
+        # Check that it gets a fresh user and a fresh clipper account
         self.assertNotEqual(old_user, new_user)
         self.assertNotEqual(old_clipper, new_clipper)
+
+        # Check that the created CAS account matches the old one
         self.assertEqual(new_clipper.cas_login, fake_cas_client.cas_login)
         self.assertEqual(new_clipper.entrance_year, fake_cas_client.entrance_year)
+
+        # Check deprecation of the old CAS account
+        old_user.refresh_from_db()
+        self.assertFalse(hasattr(old_user, "cas_account"))
+        self.assertTrue(hasattr(old_user, "old_cas_account"))
+        old_cas = old_user.old_cas_account
+        self.assertEqual(old_cas.cas_login, old_clipper.cas_login)
+        self.assertEqual(old_cas.entrance_year, old_clipper.entrance_year)
+
+
+class TestOldCASBackend(TestCase):
+    def test_simple_auth(self):
+        user = UserModel.objects.create_user(username="johndoe31", password="password")
+        wrong_user = UserModel.objects.create_user("johndoe", "password")
+        OldCASAccount.objects.create(user=user, cas_login="johndoe", entrance_year=2019)
+
+        auth_user = authenticate(
+            None, cas_login="johndoe", entrance_year=2019, password="password"
+        )
+        self.assertEqual(auth_user, user)
diff --git a/tests/settings.py b/tests/settings.py
index 82c5d96..1bcad09 100644
--- a/tests/settings.py
+++ b/tests/settings.py
@@ -16,16 +16,17 @@ INSTALLED_APPS = [
 AUTHENTICATION_BACKENDS = [
     "django.contrib.auth.backends.ModelBackend",
     "authens.backends.ENSCASBackend",
+    "authens.backends.OldCASBackend",
 ]
 
 MIDDLEWARE = [
-    'django.middleware.security.SecurityMiddleware',
-    'django.contrib.sessions.middleware.SessionMiddleware',
-    'django.middleware.common.CommonMiddleware',
-    'django.middleware.csrf.CsrfViewMiddleware',
-    'django.contrib.auth.middleware.AuthenticationMiddleware',
-    'django.contrib.messages.middleware.MessageMiddleware',
-    'django.middleware.clickjacking.XFrameOptionsMiddleware',
+    "django.middleware.security.SecurityMiddleware",
+    "django.contrib.sessions.middleware.SessionMiddleware",
+    "django.middleware.common.CommonMiddleware",
+    "django.middleware.csrf.CsrfViewMiddleware",
+    "django.contrib.auth.middleware.AuthenticationMiddleware",
+    "django.contrib.messages.middleware.MessageMiddleware",
+    "django.middleware.clickjacking.XFrameOptionsMiddleware",
 ]
 
 TEMPLATES = [