diff --git a/daphne/server.py b/daphne/server.py
index 04d01e4..e5728b3 100755
--- a/daphne/server.py
+++ b/daphne/server.py
@@ -1,6 +1,6 @@
 # This has to be done first as Twisted is import-order-sensitive with reactors
 import asyncio  # isort:skip
-import os # isort:skip
+import os  # isort:skip
 import sys  # isort:skip
 import warnings  # isort:skip
 from concurrent.futures import ThreadPoolExecutor  # isort:skip
diff --git a/tests/test_cli.py b/tests/test_cli.py
index 59b68f4..8368488 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -258,10 +258,10 @@ class TestCLIInterface(TestCase):
         self.assertCLI(["--no-server-name"], {"server_name": ""})
 
 
-@skipUnless(os.getenv('ASGI_THREADS'), "ASGI_THREADS environment variable not set.")
+@skipUnless(os.getenv("ASGI_THREADS"), "ASGI_THREADS environment variable not set.")
 class TestASGIThreads(TestCase):
     def test_default_executor(self):
         from daphne.server import twisted_loop
 
         executor = twisted_loop._default_executor
-        self.assertEqual(executor._max_workers, int(os.getenv('ASGI_THREADS')))
+        self.assertEqual(executor._max_workers, int(os.getenv("ASGI_THREADS")))