Add extensions for class-based error handler

tests/test_dispatcher/test_handler/test_error.py

@@ -0,0 +1,29 @@
+from typing import Any
+
+import pytest
+
+from aiogram.api.types import (
+    CallbackQuery,
+    InlineQuery,
+    Poll,
+    PollOption,
+    ShippingAddress,
+    ShippingQuery,
+    User,
+)
+from aiogram.dispatcher.handler import ErrorHandler, PollHandler
+
+
+class TestErrorHandler:
+    @pytest.mark.asyncio
+    async def test_extensions(self):
+        event = KeyError("kaboom")
+
+        class MyHandler(ErrorHandler):
+            async def handle(self) -> Any:
+                assert self.event == event
+                assert self.exception_name == event.__class__.__name__
+                assert self.exception_message == str(event)
+                return True
+
+        assert await MyHandler(event)