Check for async callbacks in contracts.

scrapy/contracts/__init__.py

@@ -2,7 +2,8 @@ import re
 import sys
 from functools import wraps
 from inspect import getmembers
-from typing import Dict
+from types import CoroutineType
+from typing import AsyncGenerator, Dict
 from unittest import TestCase
 
 from scrapy.http import Request
@@ -37,7 +38,10 @@ class Contract:
                 else:
                     results.addSuccess(self.testcase_pre)
                 finally:
-                    return list(iterate_spider_output(cb(response, **cb_kwargs)))
+                    cb_result = cb(response, **cb_kwargs)
+                    if isinstance(cb_result, (AsyncGenerator, CoroutineType)):
+                        raise TypeError("Contracts don't support async callbacks")
+                    return list(iterate_spider_output(cb_result))
 
             request.callback = wrapper
 
@@ -49,7 +53,10 @@ class Contract:
 
             @wraps(cb)
             def wrapper(response, **cb_kwargs):
-                output = list(iterate_spider_output(cb(response, **cb_kwargs)))
+                cb_result = cb(response, **cb_kwargs)
+                if isinstance(cb_result, (AsyncGenerator, CoroutineType)):
+                    raise TypeError("Contracts don't support async callbacks")
+                output = list(iterate_spider_output(cb_result))
                 try:
                     results.startTest(self.testcase_post)
                     self.post_process(output)

tests/test_contracts.py

@@ -63,6 +63,13 @@ class TestSpider(Spider):
         """
         return Request("http://scrapy.org", callback=self.returns_item)
 
+    async def returns_request_async(self, response):
+        """async method which returns request
+        @url http://scrapy.org
+        @returns requests 1
+        """
+        return Request("http://scrapy.org", callback=self.returns_item)
+
     def returns_item(self, response):
         """method which returns item
         @url http://scrapy.org
@@ -337,6 +344,14 @@ class ContractsManagerTest(unittest.TestCase):
         request.callback(response)
         self.should_fail()
 
+    def test_returns_async(self):
+        spider = TestSpider()
+        response = ResponseMock()
+
+        request = self.conman.from_method(spider.returns_request_async, self.results)
+        request.callback(response)
+        self.should_error()
+
     def test_scrapes(self):
         spider = TestSpider()
         response = ResponseMock()