diff --git a/tests/HTTP/SapiTest.php b/tests/HTTP/SapiTest.php
index 444832b..bde63d8 100644
--- a/tests/HTTP/SapiTest.php
+++ b/tests/HTTP/SapiTest.php
@@ -309,6 +309,7 @@ public function testSendConnectionAborted(): void
         $fetch_size = 6 * 1024 * 1024;
 
         $stream = fopen($url, 'r');
+        self::assertIsResource($stream, "could not open $url - is the test server running?");
         $size = 0;
 
         while ($size <= $fetch_size) {