diff --git a/tests/test_utils_asyncgen.py b/tests/test_utils_asyncgen.py
index 7f9c0371b..1e4dfbaf9 100644
--- a/tests/test_utils_asyncgen.py
+++ b/tests/test_utils_asyncgen.py
@@ -1,38 +1,44 @@
 import sys
-from unittest import TestCase
 
 from pytest import mark
+from twisted.trial import unittest
+
+from scrapy.utils.defer import deferred_f_from_coro_f
 
 
 @mark.skipif(sys.version_info < (3, 6), reason="Async generators require Python 3.6 or higher")
-class AsyncGeneratorTest(TestCase):
+class AsyncGeneratorTest(unittest.TestCase):
 
+    @deferred_f_from_coro_f
     async def test_as_async_generator_simple(self):
         from scrapy.utils.asyncgen import as_async_generator
         gen = (i for i in range(3))
         results = []
         async for i in as_async_generator(gen):
             results.append(i)
-        self.assertEqual(results, [1, 2, 3])
+        self.assertEqual(results, [0, 1, 2])
 
+    @deferred_f_from_coro_f
     async def test_as_async_generator_list(self):
         from scrapy.utils.asyncgen import as_async_generator
         L = [i for i in range(3)]
         results = []
         async for i in as_async_generator(L):
             results.append(i)
-        self.assertEqual(results, [1, 2, 3])
+        self.assertEqual(results, [0, 1, 2])
 
+    @deferred_f_from_coro_f
     async def test_as_async_generator_async(self):
         from scrapy.utils.asyncgen import as_async_generator
         from tests.py36._test_utils_asyncgen import async_gen
         results = []
         async for i in as_async_generator(async_gen()):
             results.append(i)
-        self.assertEqual(results, [1, 2, 3])
+        self.assertEqual(results, [0, 1, 2])
 
+    @deferred_f_from_coro_f
     async def test_collect_asyncgen(self):
         from scrapy.utils.asyncgen import collect_asyncgen
         from tests.py36._test_utils_asyncgen import async_gen
-        results = collect_asyncgen(async_gen())
-        self.assertEqual(results, [1, 2, 3])
+        results = await collect_asyncgen(async_gen())
+        self.assertEqual(results, [0, 1, 2])