Add a test for an async item_scraped handler.

tests/test_signals.py

@@ -0,0 +1,39 @@
+from twisted.internet import defer
+from twisted.trial import unittest
+
+from scrapy import signals, Request, Spider
+from scrapy.utils.test import get_crawler
+
+from tests.mockserver import MockServer
+
+
+class ItemSpider(Spider):
+    name = 'itemspider'
+
+    def start_requests(self):
+        for _ in range(10):
+            yield Request(self.mockserver.url('/status?n=200'),
+                          dont_filter=True)
+
+    def parse(self, response):
+        return {'field': 42}
+
+
+class AsyncSignalTestCase(unittest.TestCase):
+    def setUp(self):
+        self.mockserver = MockServer()
+        self.mockserver.__enter__()
+        self.items = []
+
+    def tearDown(self):
+        self.mockserver.__exit__(None, None, None)
+
+    async def _on_item_scraped(self, item):
+        self.items.append(item)
+
+    @defer.inlineCallbacks
+    def test_simple_pipeline(self):
+        crawler = get_crawler(ItemSpider)
+        crawler.signals.connect(self._on_item_scraped, signals.item_scraped)
+        yield crawler.crawl(mockserver=self.mockserver)
+        self.assertEqual(len(self.items), 10)