diff --git a/channels/layers.py b/channels/layers.py
index 20b91c43..1f418544 100644
--- a/channels/layers.py
+++ b/channels/layers.py
@@ -147,10 +147,13 @@ class BaseChannelLayer(ABC):
 
     MAX_NAME_LENGTH = 100
     extensions: Iterable[str] = ()
+    expiry: int
+    capacity: int
+    channel_capacity: Dict[str, int]
 
     def __init__(
         self,
-        expiry=60,
+        expiry: int = 60,
         capacity: Optional[int] = 100,
         channel_capacity: Optional[int] = None,
     ):
@@ -263,7 +266,12 @@ async def new_channel(self, prefix: str = "specific.") -> str:
         """
 
 
-class InMemoryChannelLayer(WithFlushExtension, WithGroupsExtension, BaseChannelLayer):
+# WARNING: Protocols must be last
+class InMemoryChannelLayer(
+    BaseChannelLayer,
+    WithFlushExtension,
+    WithGroupsExtension,
+):
     """
     In-memory channel layer implementation
     """
diff --git a/tests/test_layers.py b/tests/test_layers.py
index 543a9f19..3ebbc287 100644
--- a/tests/test_layers.py
+++ b/tests/test_layers.py
@@ -13,6 +13,18 @@
 )
 
 
+# when starting with Test it would be tried to collect by pytest
+class StubChannelLayer(BaseChannelLayer):
+    async def send(self, channel: str, message: dict):
+        raise NotImplementedError()
+
+    async def receive(self, channel: str) -> dict:
+        raise NotImplementedError()
+
+    async def new_channel(self, prefix: str = "specific.") -> str:
+        raise NotImplementedError()
+
+
 class TestChannelLayerManager(unittest.TestCase):
     @override_settings(
         CHANNEL_LAYERS={"default": {"BACKEND": "channels.layers.InMemoryChannelLayer"}}
@@ -72,7 +84,7 @@ async def test_send_receive():
 
 @pytest.mark.parametrize(
     "method",
-    [BaseChannelLayer().valid_channel_name, BaseChannelLayer().valid_group_name],
+    [StubChannelLayer().valid_channel_name, StubChannelLayer().valid_group_name],
 )
 @pytest.mark.parametrize(
     "channel_name,expected_valid",