diff --git a/tests/conftest.py b/tests/conftest.py
index b73202cd..905f3f4b 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -107,10 +107,12 @@ def dev_server(xprocess, request, tmp_path):
             # Unbuffered output so the logs update immediately.
             env = {**os.environ, "PYTHONPATH": str(tmp_path), "PYTHONUNBUFFERED": "1"}
 
-            @cached_property
-            def pattern(self):
-                client.request("/ensure")
-                return "GET /ensure"
+            def startup_check(self):
+                try:
+                    client.request("/ensure")
+                    return True
+                except (ConnectionRefusedError, FileNotFoundError):
+                    return False
 
         # Each test that uses the fixture will have a different log.
         xp_name = f"dev_server-{request.node.name}"