Allow empty and zero parts in CallbackData (#646)

* enh: allow empty parts in CallbackData

* enh: allow zero parts in CallbackData

* new: tests for CallbackData

tests/test_utils/test_callback_data.py

@@ -0,0 +1,39 @@
+import pytest
+
+from aiogram.types import CallbackQuery
+from aiogram.utils.callback_data import CallbackData
+
+
+class TestCallbackData:
+    @pytest.mark.asyncio
+    async def test_cb(self):
+        cb = CallbackData('simple', 'action')
+        assert cb.new('x') == 'simple:x'
+        assert cb.new(action='y') == 'simple:y'
+        assert cb.new('') == 'simple:'
+
+        assert (await cb.filter().check(CallbackQuery(data='simple:'))) == {'callback_data': {'@': 'simple', 'action': ''}}
+        assert (await cb.filter().check(CallbackQuery(data='simple:x'))) == {'callback_data': {'@': 'simple', 'action': 'x'}}
+        assert (await cb.filter(action='y').check(CallbackQuery(data='simple:x'))) is False
+
+    @pytest.mark.asyncio
+    async def test_cb_double(self):
+        cb = CallbackData('double', 'pid', 'action')
+        assert cb.new('123', 'x') == 'double:123:x'
+        assert cb.new(pid=456, action='y') == 'double:456:y'
+        assert cb.new('', 'z') == 'double::z'
+        assert cb.new('789', '') == 'double:789:'
+
+        assert (await cb.filter().check(CallbackQuery(data='double::'))) == {'callback_data': {'@': 'double', 'pid': '', 'action': ''}}
+        assert (await cb.filter().check(CallbackQuery(data='double:x:'))) == {'callback_data': {'@': 'double', 'pid': 'x', 'action': ''}}
+        assert (await cb.filter().check(CallbackQuery(data='double::y'))) == {'callback_data': {'@': 'double', 'pid': '', 'action': 'y'}}
+        assert (await cb.filter(action='x').check(CallbackQuery(data='double:123:x'))) == {'callback_data': {'@': 'double', 'pid': '123', 'action': 'x'}}
+
+    @pytest.mark.asyncio
+    async def test_cb_zero(self):
+        cb = CallbackData('zero')
+        assert cb.new() == 'zero'
+
+        assert (await cb.filter().check(CallbackQuery(data='zero'))) == {'callback_data': {'@': 'zero'}}
+        assert (await cb.filter().check(CallbackQuery(data='zero:'))) is False
+        assert (await cb.filter().check(CallbackQuery(data='bla'))) is False