Reliability improvements

scrapy/core/engine.py

@@ -198,6 +198,8 @@ class ExecutionEngine:
                 exc_info=True,
             )
         else:
+            if not self.spider:
+                return  # spider already closed
             if isinstance(item_or_request, Request):
                 self.crawl(item_or_request)
             else:
@@ -219,7 +221,7 @@ class ExecutionEngine:
         self._slot.nextcall.schedule()
         self._slot.heartbeat.start(self._SLOT_HEARTBEAT_INTERVAL)
 
-        while self._start is not None:
+        while self._start and self.spider:
             await self._process_start_next()
             if not self.needs_backout():
                 # Give room for the outcome of self._process_start_next() to be

tests/test_engine_loop.py

@@ -109,9 +109,6 @@ class RequestSendOrderTestCase(TestCase):
     that can be sent before the first callback requests are scheduled.
     """
 
-    # Error out if any tests relies on the heartbeat.
-    timeout = ExecutionEngine._SLOT_HEARTBEAT_INTERVAL
-
     @classmethod
     def setUpClass(cls):
         cls.mockserver = MockServer()
@@ -122,7 +119,7 @@ class RequestSendOrderTestCase(TestCase):
         cls.mockserver.__exit__(None, None, None)
 
     fast_seconds = 0.001
-    slow_seconds = 1  # increase if flaky
+    slow_seconds = 2  # increase if flaky
 
     def _request(self, num, response_seconds, download_slots):
         url = self.mockserver.url(f"/delay?n={response_seconds}&{num}")