diff --git a/aioresponses/core.py b/aioresponses/core.py
index 48426b4..566e678 100644
--- a/aioresponses/core.py
+++ b/aioresponses/core.py
@@ -40,7 +40,6 @@
     RequestInfo, AIOHTTP_VERSION,
 )
 
-
 _FuncT = TypeVar("_FuncT", bound=Callable[..., Any])
 
 
@@ -224,7 +223,7 @@ def __repr__(self) -> str:
 class aioresponses(object):
     """Mock aiohttp requests made by ClientSession."""
     _matches = None  # type: Dict[str, RequestMatch]
-    _responses = None  # type: List[ClientResponse]
+    _responses: List[ClientResponse] = None
     requests = None  # type: Dict
 
     def __init__(self, **kwargs: Any):
diff --git a/requirements-dev.txt b/requirements-dev.txt
index bb31c52..04cea66 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -1,6 +1,6 @@
 pip
 wheel
-flake8==3.8.3
+flake8==5.0.4
 tox==3.19.0
 coverage==5.2.1
 Sphinx==1.5.6
@@ -10,5 +10,4 @@ pytest-html==2.1.1
 ddt==1.4.1
 typing
 asynctest==0.13.0
-yarl==1.9.4
-setuptools==69.5.1
+yarl==1.9.4
\ No newline at end of file
diff --git a/setup.cfg b/setup.cfg
index 0b0fe1d..9db058d 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -35,6 +35,7 @@ universal = 1
 
 [flake8]
 exclude = docs
+max-line-length = 120
 
 [tool:pytest]
 testpaths = tests
diff --git a/tests/test_aioresponses.py b/tests/test_aioresponses.py
index 23fce89..865d73b 100644
--- a/tests/test_aioresponses.py
+++ b/tests/test_aioresponses.py
@@ -86,6 +86,7 @@ async def test_returned_instance_and_status_code(self, m):
         ("http://example.com/", "/api?foo=bar#fragment")
     )
     @aioresponses()
+    @skipIf(condition=AIOHTTP_VERSION < Version('3.8.0'), reason='aiohttp must be >= 3.8.0')
     async def test_base_url(self, base_url, relative_url, m):
         m.get(self.url, status=200)
         self.session = ClientSession(base_url=base_url)