tests: mark trailing slash test as xfail (#1138)

Author: felixweinberger

tests/client/test_auth.py

@@ -836,16 +836,20 @@ async def test_token_exchange_error_basic(self, oauth_provider, oauth_client_inf
         "revocation_endpoint",
     ),
     (
-        # TODO(Marcelo): Since we are using `AnyUrl`, the trailing slash is always added.
-        # pytest.param(
-        #     "https://auth.example.com",
-        #     "https://auth.example.com/docs",
-        #     "https://auth.example.com/authorize",
-        #     "https://auth.example.com/token",
-        #     "https://auth.example.com/register",
-        #     "https://auth.example.com/revoke",
-        #     id="simple-url",
-        # ),
+        # Pydantic's AnyUrl incorrectly adds trailing slash to base URLs
+        # This is being fixed in https://github.com/pydantic/pydantic-core/pull/1719 (Pydantic 2.12+)
+        pytest.param(
+            "https://auth.example.com",
+            "https://auth.example.com/docs",
+            "https://auth.example.com/authorize",
+            "https://auth.example.com/token",
+            "https://auth.example.com/register",
+            "https://auth.example.com/revoke",
+            id="simple-url",
+            marks=pytest.mark.xfail(
+                reason="Pydantic AnyUrl adds trailing slash to base URLs - fixed in Pydantic 2.12+"
+            ),
+        ),
         pytest.param(
             "https://auth.example.com/",
             "https://auth.example.com/docs",