Dev 3.x flat package (#961)

* Move packages

* Added changelog

* Update examples/echo_bot.py

Co-authored-by: Oleg A. <t0rr@mail.ru>

* Rename `handler` -> `handlers`

* Update __init__.py

Co-authored-by: Oleg A. <t0rr@mail.ru>

tests/test_handler/test_base.py

@@ -0,0 +1,64 @@
+import asyncio
+import datetime
+from functools import wraps
+from typing import Any
+
+import pytest
+
+from aiogram import Bot
+from aiogram.dispatcher.event.handler import HandlerObject
+from aiogram.handlers import BaseHandler
+from aiogram.types import Chat, Message, Update
+
+pytestmark = pytest.mark.asyncio
+
+
+class MyHandler(BaseHandler):
+    async def handle(self) -> Any:
+        await asyncio.sleep(0.1)
+        return 42
+
+
+class TestBaseClassBasedHandler:
+    async def test_base_handler(self):
+        event = Update(update_id=42)
+        handler = MyHandler(event=event, key=42)
+
+        assert handler.event == event
+        assert handler.data["key"] == 42
+        assert not hasattr(handler, "filters")
+        assert await handler == 42
+
+    async def test_bot_from_context(self):
+        event = Update(update_id=42)
+        handler = MyHandler(event=event, key=42)
+        bot = Bot("42:TEST")
+
+        with pytest.raises(LookupError):
+            handler.bot
+
+        Bot.set_current(bot)
+        assert handler.bot == bot
+
+    async def test_bot_from_data(self):
+        event = Update(update_id=42)
+        bot = Bot("42:TEST")
+        handler = MyHandler(event=event, key=42, bot=bot)
+
+        assert "bot" in handler.data
+        assert handler.bot == bot
+
+    def test_update_from_data(self):
+        event = Message(
+            message_id=42, chat=Chat(id=42, type="private"), date=datetime.datetime.now()
+        )
+        update = Update(update_id=42, message=event)
+        handler = MyHandler(event=event, update=update)
+
+        assert handler.event == event
+        assert handler.update == update
+
+    async def test_wrapped_handler(self):
+        # wrap the handler on dummy function
+        handler = wraps(MyHandler)(lambda: None)
+        assert HandlerObject(handler).awaitable is True