diff --git a/src/flask/testing.py b/src/flask/testing.py
index a62c4836..da156cc1 100644
--- a/src/flask/testing.py
+++ b/src/flask/testing.py
@@ -58,9 +58,9 @@ class EnvironBuilder(werkzeug.test.EnvironBuilder):
     ) -> None:
         assert not (base_url or subdomain or url_scheme) or (
             base_url is not None
-        ) != bool(
-            subdomain or url_scheme
-        ), 'Cannot pass "subdomain" or "url_scheme" with "base_url".'
+        ) != bool(subdomain or url_scheme), (
+            'Cannot pass "subdomain" or "url_scheme" with "base_url".'
+        )
 
         if base_url is None:
             http_host = app.config.get("SERVER_NAME") or "localhost"