diff --git a/.travis.yml b/.travis.yml
index 6bde973f4..cb54c8008 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -15,19 +15,25 @@ matrix:
       python: 3.7  # Keep in sync with .readthedocs.yml
 
     - env: TOXENV=pypy3
-    - python: 3.5
+    - env: TOXENV=py
+      python: 3.5
     - env: TOXENV=pinned
       python: 3.5
     - env: TOXENV=asyncio
       python: 3.5.2
-    - python: 3.6
-    - python: 3.7
-    - env: PYPI_RELEASE_JOB=true
+    - env: TOXENV=py
+      python: 3.6
+    - env: TOXENV=py
+      python: 3.7
+    - env: TOXENV=py PYPI_RELEASE_JOB=true
       python: 3.8
+      dist: bionic
     - env: TOXENV=extra-deps
       python: 3.8
+      dist: bionic
     - env: TOXENV=asyncio
       python: 3.8
+      dist: bionic
 install:
   - |
       if [ "$TOXENV" = "pypy3" ]; then
diff --git a/pytest.ini b/pytest.ini
index 7c3c9cc5b..44b0e070c 100644
--- a/pytest.ini
+++ b/pytest.ini
@@ -109,7 +109,7 @@ flake8-ignore =
     # scrapy/spidermiddlewares
     scrapy/spidermiddlewares/httperror.py E501
     scrapy/spidermiddlewares/offsite.py E501
-    scrapy/spidermiddlewares/referer.py E501 E129
+    scrapy/spidermiddlewares/referer.py E501
     scrapy/spidermiddlewares/urllength.py E501
     # scrapy/spiders
     scrapy/spiders/__init__.py E501 E402
@@ -233,7 +233,7 @@ flake8-ignore =
     tests/test_utils_defer.py E501 F841
     tests/test_utils_deprecate.py F841 E501
     tests/test_utils_http.py E501
-    tests/test_utils_iterators.py E501 E129
+    tests/test_utils_iterators.py E501
     tests/test_utils_log.py E741
     tests/test_utils_python.py E501
     tests/test_utils_reqser.py E501
diff --git a/scrapy/spiderloader.py b/scrapy/spiderloader.py
index 8dc89c2e9..63da55718 100644
--- a/scrapy/spiderloader.py
+++ b/scrapy/spiderloader.py
@@ -1,7 +1,7 @@
 # -*- coding: utf-8 -*-
-from collections import defaultdict
 import traceback
 import warnings
+from collections import defaultdict
 
 from zope.interface import implementer
 
@@ -16,6 +16,7 @@ class SpiderLoader:
     SpiderLoader is a class which locates and loads spiders
     in a Scrapy project.
     """
+
     def __init__(self, settings):
         self.spider_modules = settings.getlist('SPIDER_MODULES')
         self.warn_only = settings.getbool('SPIDER_LOADER_WARN_ONLY')
@@ -29,13 +30,16 @@ class SpiderLoader:
             dupes.extend([
                 "  {cls} named {name!r} (in {module})".format(module=mod, cls=cls, name=name)
                 for mod, cls in locations
+                if len(locations) > 1
             ])
 
         if dupes:
             dupes_string = "\n\n".join(dupes)
-            msg = ("There are several spiders with the same name:\n\n"
-                   "{}\n\n  This can cause unexpected behavior.".format(dupes_string))
-            warnings.warn(msg, UserWarning)
+            warnings.warn(
+                "There are several spiders with the same name:\n\n"
+                "{}\n\n  This can cause unexpected behavior.".format(dupes_string),
+                category=UserWarning,
+            )
 
     def _load_spiders(self, module):
         for spcls in iter_spider_classes(module):
@@ -49,11 +53,13 @@ class SpiderLoader:
                     self._load_spiders(module)
             except ImportError:
                 if self.warn_only:
-                    msg = (
+                    warnings.warn(
                         "\n{tb}Could not load spiders from module '{modname}'. "
-                        "See above traceback for details.".format(modname=name, tb=traceback.format_exc())
+                        "See above traceback for details.".format(
+                            modname=name, tb=traceback.format_exc()
+                        ),
+                        category=RuntimeWarning,
                     )
-                    warnings.warn(msg, RuntimeWarning)
                 else:
                     raise
         self._check_name_duplicates()
@@ -76,8 +82,10 @@ class SpiderLoader:
         """
         Return the list of spider names that can handle the given request.
         """
-        return [name for name, cls in self._spiders.items()
-                if cls.handles_request(request)]
+        return [
+            name for name, cls in self._spiders.items()
+            if cls.handles_request(request)
+        ]
 
     def list(self):
         """
diff --git a/tests/test_crawler.py b/tests/test_crawler.py
index b4144ea1d..9151278a5 100644
--- a/tests/test_crawler.py
+++ b/tests/test_crawler.py
@@ -311,14 +311,7 @@ class CrawlerProcessSubprocess(ScriptRunnerMixin, unittest.TestCase):
     def test_ipv6_alternative_name_resolver(self):
         log = self.run_script('alternative_name_resolver.py')
         self.assertIn('Spider closed (finished)', log)
-        self.assertTrue(any([
-            "twisted.internet.error.ConnectionRefusedError" in log,
-            "twisted.internet.error.ConnectError" in log,
-        ]))
-        self.assertTrue(any([
-            "'downloader/exception_type_count/twisted.internet.error.ConnectionRefusedError': 1," in log,
-            "'downloader/exception_type_count/twisted.internet.error.ConnectError': 1," in log,
-        ]))
+        self.assertNotIn("twisted.internet.error.DNSLookupError", log)
 
     def test_reactor_select(self):
         log = self.run_script("twisted_reactor_select.py")
diff --git a/tests/test_utils_iterators.py b/tests/test_utils_iterators.py
index c677dabe5..3a58cc36b 100644
--- a/tests/test_utils_iterators.py
+++ b/tests/test_utils_iterators.py
@@ -92,8 +92,8 @@ class XmliterTestCase(unittest.TestCase):
             # with bytes
             XmlResponse(url="http://example.com", body=body.encode('utf-8')),
             # Unicode body needs encoding information
-            XmlResponse(url="http://example.com", body=body, encoding='utf-8')):
-
+            XmlResponse(url="http://example.com", body=body, encoding='utf-8'),
+        ):
             attrs = []
             for x in self.xmliter(r, u'þingflokkur'):
                 attrs.append((x.attrib['id'],
diff --git a/tox.ini b/tox.ini
index 697328ebd..2102fc602 100644
--- a/tox.ini
+++ b/tox.ini
@@ -4,7 +4,7 @@
 # and then run "tox" from this directory.
 
 [tox]
-envlist = security,flake8,py3
+envlist = security,flake8,py
 minversion = 1.7.0
 
 [testenv]