diff --git a/src/auth_server/tests/test_saml_sp.py b/src/auth_server/tests/test_saml_sp.py
index eb10f24..0be7d35 100644
--- a/src/auth_server/tests/test_saml_sp.py
+++ b/src/auth_server/tests/test_saml_sp.py
@@ -3,7 +3,7 @@
 from datetime import datetime, timedelta
 from os import environ
 from pathlib import Path
-from typing import Any, Dict, Mapping
+from typing import Any, Dict, Mapping, Optional
 from unittest import TestCase
 from urllib.parse import parse_qs, urlparse
 
@@ -191,6 +191,14 @@ def setUp(self) -> None:
           </saml2p:Status>
         </saml2p:Response>"""
 
+    def _update_app_config(self, config: Optional[Dict] = None):
+        if config is not None:
+            environ.clear()
+            environ.update(config)
+        self._clear_lru_cache()
+        self.app = init_auth_server_api()
+        self.client = TestClient(self.app)
+
     @staticmethod
     def _clear_lru_cache():
         # Clear lru_cache to allow config update
@@ -248,8 +256,10 @@ def get_current_saml_request_id(self) -> str:
         return ids[0]
 
     def test_authn_request(self):
+        self.config["saml2_single_idp"] = self.test_idp
+        self._update_app_config(config=self.config)
         authn_url = saml2_router.url_path_for("authenticate", transaction_id=self.test_transaction_state.transaction_id)
-        response = self.client.get(f"{authn_url}?idp={self.test_idp}", allow_redirects=False)
+        response = self.client.get(authn_url, allow_redirects=False)
         assert response.status_code == 303
         assert (
             response.headers["location"].startswith(
@@ -259,6 +269,8 @@ def test_authn_request(self):
         )
 
     def test_saml_acs(self):
+        self.config["saml2_single_idp"] = self.test_idp
+        self._update_app_config(config=self.config)
         # do authn request
         authn_url = saml2_router.url_path_for("authenticate", transaction_id=self.test_transaction_state.transaction_id)
         self.client.get(f"{authn_url}?idp={self.test_idp}", allow_redirects=False)
@@ -272,7 +284,7 @@ def test_saml_acs(self):
             saml2_router.url_path_for("assertion_consumer_service"), data=data, follow_redirects=False
         )
         assert response.status_code == 303
-        assert response.headers["location"].startswith("/interaction/redirect/") is True
+        assert response.headers["location"].startswith("http://testserver/interaction/redirect/") is True
 
         # check authentication result
         transaction_state = self._get_transaction_state_by_id(self.test_transaction_state.transaction_id)