Check bot instance on Dispatcher __init__

tests/test_dispatcher.py

@@ -0,0 +1,35 @@
+from aiogram import Dispatcher, Bot
+
+import pytest
+
+pytestmark = pytest.mark.asyncio
+
+
+@pytest.yield_fixture()
+async def bot(event_loop):
+    """ Bot fixture """
+    _bot = Bot(token='123456789:AABBCCDDEEFFaabbccddeeff-1234567890',
+               loop=event_loop)
+    yield _bot
+    await _bot.close()
+
+
+class TestDispatcherInit:
+    async def test_successful_init(self, bot):
+        """
+        Success __init__ case
+
+        :param bot: bot instance
+        :type bot: Bot
+        """
+        dp = Dispatcher(bot=bot)
+        assert isinstance(dp, Dispatcher)
+
+    @pytest.mark.parametrize("bot_instance", [None, Bot, 123, 'abc'])
+    async def test_wrong_bot_instance(self, bot_instance):
+        """
+        User provides wrong data to 'bot' argument.
+        :return: TypeError with reason
+        """
+        with pytest.raises(TypeError):
+            _ = Dispatcher(bot=bot_instance)