diff --git a/aiogram/dispatcher/_typedef.py b/aiogram/dispatcher/_typedef.py
index 03928ce3..5cec07bc 100644
--- a/aiogram/dispatcher/_typedef.py
+++ b/aiogram/dispatcher/_typedef.py
@@ -1,6 +1,6 @@
 from typing import TYPE_CHECKING, Any, Mapping, TypeVar
 
-if TYPE_CHECKING:
+if TYPE_CHECKING:  # pragma: no cover
     StorageDataT = TypeVar("StorageDataT", bound=Mapping[str, Any])
 else:
     StorageDataT = TypeVar("StorageDataT", bound=Mapping)
diff --git a/aiogram/dispatcher/state/context.py b/aiogram/dispatcher/state/context.py
index 757f1d6f..acf7f41d 100644
--- a/aiogram/dispatcher/state/context.py
+++ b/aiogram/dispatcher/state/context.py
@@ -7,7 +7,7 @@ from .._typedef import StorageDataT
 
 def _default_key_maker(chat_id: Optional[int] = None, user_id: Optional[int] = None) -> str:
     if chat_id is None and user_id is None:
-        raise ValueError("`user` or `chat` parameter is required but no one is provided!")
+        raise ValueError("`user_id` or `chat_id` parameter is required but no one is provided!")
 
     if user_id is None and chat_id is not None:
         user_id = chat_id
@@ -26,12 +26,8 @@ class CurrentUserContext(Generic[StorageDataT]):
         user_id: Optional[int],
         key_maker: Callable[[Optional[int], Optional[int]], str] = _default_key_maker,
     ):
-        assert (
-            chat_id or user_id
-        ) is not None, "Either chat_id or user_id should be non-None value"
-
-        self.storage = storage
         self.key = key_maker(chat_id, user_id)
+        self.storage = storage
 
     async def get_state(self) -> Optional[str]:
         return await self.storage.get_state(self.key)
@@ -41,12 +37,14 @@ class CurrentUserContext(Generic[StorageDataT]):
 
     async def update_data(self, data: Optional[StorageDataT] = None, **kwargs: Any) -> None:
         if data is not None and not isinstance(data, Mapping):
-            raise ValueError("Data is expected to be a map")  # todo
+            raise ValueError(
+                "type for `data` is expected to be a subtype of `collections.Mapping`"
+            )
 
         temp_data: Dict[str, Any] = {}
 
         if isinstance(data, Mapping):
-            temp_data.update(**data)
+            temp_data.update(data)
 
         temp_data.update(**kwargs)
 
diff --git a/aiogram/dispatcher/storage/base.py b/aiogram/dispatcher/storage/base.py
index f76f9181..81215ab8 100644
--- a/aiogram/dispatcher/storage/base.py
+++ b/aiogram/dispatcher/storage/base.py
@@ -1,5 +1,4 @@
 import abc
-
 from typing import Generic, Optional, TypeVar
 
 _DataT = TypeVar("_DataT")
diff --git a/aiogram/dispatcher/storage/dict.py b/aiogram/dispatcher/storage/dict.py
index f6ceaf86..6966f7eb 100644
--- a/aiogram/dispatcher/storage/dict.py
+++ b/aiogram/dispatcher/storage/dict.py
@@ -44,7 +44,7 @@ class DictStorage(BaseStorage[Dict[str, Any]]):
 
     async def set_data(self, key: str, data: Optional[Dict[str, Any]] = None) -> None:
         self._make_spot_for_key(key=key)
-        self._data[key]["data"] = copy.deepcopy(data)  # type: ignore
+        self._data[key]["data"] = copy.deepcopy(data) or {}  # type: ignore
 
     async def wait_closed(self) -> None:
         pass
diff --git a/tests/test_dispatcher/test_state/__init__.py b/tests/test_dispatcher/test_state/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/tests/test_dispatcher/test_state/test_context.py b/tests/test_dispatcher/test_state/test_context.py
new file mode 100644
index 00000000..6f0dc132
--- /dev/null
+++ b/tests/test_dispatcher/test_state/test_context.py
@@ -0,0 +1,118 @@
+import contextlib
+from collections import Mapping
+
+import pytest
+
+from aiogram.dispatcher.state.context import CurrentUserContext, _default_key_maker
+from aiogram.dispatcher.storage.dict import DictStorage
+
+try:
+    from asynctest import CoroutineMock, patch
+except ImportError:
+    from unittest.mock import AsyncMock as CoroutineMock, patch  # type: ignore
+
+
+@pytest.fixture(scope="function")
+def storage() -> DictStorage:
+    return DictStorage()
+
+
+@contextlib.contextmanager
+def patch_dict_storage_method(method: str):
+    with patch(
+        f"aiogram.dispatcher.storage.dict.DictStorage.{method}", new_callable=CoroutineMock,
+    ) as mocked:
+        yield mocked
+
+
+def test_default_key_maker():
+    chat_id, user_id = None, None
+    with pytest.raises(ValueError):
+        _default_key_maker(chat_id, user_id)
+
+    chat_id, user_id = 1, None
+    assert _default_key_maker(chat_id, user_id) == f"{chat_id}:{chat_id}"
+
+    chat_id, user_id = None, 1
+    assert _default_key_maker(chat_id, user_id) == f"{user_id}:{user_id}"
+
+    chat_id, user_id = 2 ** 8, 2 ** 10
+    assert _default_key_maker(chat_id, user_id) == f"{chat_id}:{user_id}"
+
+
+class TestCurrentUserContext:
+    def test_init(self, storage):
+        chat_id, user_id = 1, 2
+        ctx = CurrentUserContext(storage, chat_id, user_id)
+        assert not hasattr(ctx, "__dict__")
+        assert ctx.storage == storage
+        assert ctx.key == _default_key_maker(chat_id, user_id)
+
+    def test_custom_key_maker(self, storage):
+        key_maker_const_result = "mpa"
+
+        def my_key_maker(chat_id: int, user_id: int):
+            return key_maker_const_result
+
+        chat_id, user_id = 1, 2
+        ctx = CurrentUserContext(storage, chat_id, user_id, key_maker=my_key_maker)
+        assert ctx.key == my_key_maker(chat_id, user_id) == key_maker_const_result
+
+    @pytest.mark.asyncio
+    @pytest.mark.parametrize("setter_method", ("set_state", "set_data"))
+    async def test_setters(self, storage, setter_method):
+        chat_id, user_id = 1, 2
+        ctx = CurrentUserContext(storage, chat_id, user_id)
+
+        with patch_dict_storage_method(setter_method) as mocked:
+            await getattr(ctx, setter_method)("some")
+            mocked.assert_awaited()
+
+    @pytest.mark.asyncio
+    @pytest.mark.parametrize("getter_method", ("set_state", "set_data"))
+    async def test_getters(self, storage, getter_method):
+        chat_id, user_id = 1, 2
+        ctx = CurrentUserContext(storage, chat_id, user_id)
+
+        with patch_dict_storage_method(getter_method) as mocked:
+            await getattr(ctx, getter_method)()
+            mocked.assert_awaited()
+
+    @pytest.mark.asyncio
+    @pytest.mark.parametrize("reseter_method", ("reset_data", "reset_state", "finish"))
+    async def test_setters(self, storage, reseter_method):
+        chat_id, user_id = 1, 2
+        ctx = CurrentUserContext(storage, chat_id, user_id)
+
+        with patch_dict_storage_method(reseter_method) as mocked:
+            await getattr(ctx, reseter_method)()
+            mocked.assert_awaited()
+
+    @pytest.mark.asyncio
+    async def test_update_data(self, storage):
+        chat_id, user_id = 1, 2
+        ctx = CurrentUserContext(storage, chat_id, user_id)
+
+        with patch_dict_storage_method("update_data") as mocked:
+            await ctx.update_data()
+            mocked.assert_awaited()
+
+        with pytest.raises(
+            ValueError,
+            match="type for `data` is expected to be a subtype of `collections.Mapping`",
+        ):
+            await ctx.update_data(data="definetely not mapping")
+
+        class LegitMapping(Mapping):
+            def __getitem__(self, k):
+                return "value"
+
+            def __len__(self):
+                return 1
+
+            def __iter__(self):
+                yield "key"
+
+        new_data = LegitMapping()
+        assert await ctx.update_data(data=new_data) is None
+        assert await ctx.get_data() == new_data
diff --git a/tests/test_dispatcher/test_storage/test_base.py b/tests/test_dispatcher/test_storage/test_base.py
new file mode 100644
index 00000000..37fc6103
--- /dev/null
+++ b/tests/test_dispatcher/test_storage/test_base.py
@@ -0,0 +1,56 @@
+from typing import Any, Optional
+
+import pytest
+
+from aiogram.dispatcher.storage.base import BaseStorage
+
+try:
+    from asynctest import CoroutineMock, patch
+except ImportError:
+    from unittest.mock import AsyncMock as CoroutineMock, patch  # type: ignore
+
+
+STORAGE_ABSTRACT_METHODS = {
+    "get_data",
+    "get_state",
+    "set_data",
+    "set_state",
+    "update_data",
+    "close",
+    "wait_closed",
+}
+
+
+class TestBaseStorage:
+    def test_do_not_impl_abstract_methods(self):
+        with pytest.raises(TypeError):
+
+            class etcd(BaseStorage):  # example of bad not implemented storage
+                nothing = lambda: None
+
+            etcd()
+
+    def test_do_impl_abstract_methods(self):
+        class good(BaseStorage):
+            async def get_state(self, key: str) -> Optional[str]:
+                pass
+
+            async def set_state(self, key: str, state: Optional[str]) -> None:
+                pass
+
+            async def get_data(self, key: str) -> Any:
+                pass
+
+            async def set_data(self, key: str, data: Optional[Any]) -> None:
+                pass
+
+            async def update_data(self, key: str, data: Any) -> None:
+                pass
+
+            async def close(self) -> None:
+                pass
+
+            async def wait_closed(self) -> None:
+                pass
+
+        good()
diff --git a/tests/test_dispatcher/test_storage/test_dict.py b/tests/test_dispatcher/test_storage/test_dict.py
new file mode 100644
index 00000000..7961161f
--- /dev/null
+++ b/tests/test_dispatcher/test_storage/test_dict.py
@@ -0,0 +1,76 @@
+from typing import Dict
+
+import pytest
+
+from aiogram.dispatcher.storage.dict import DictStorage
+
+
+class TestDictStorage:
+    def test_init(self):
+        storage: DictStorage[Dict[str, str]] = DictStorage()
+        assert not storage._data
+        assert isinstance(storage._data, dict)
+
+    def test_key_resolution(self):
+        storage: DictStorage[Dict[str, str]] = DictStorage()
+        key = "L:R"
+        assert key not in storage._data
+        storage._make_spot_for_key(key)
+        assert key in storage._data
+        assert storage._data.get(key) == {"state": None, "data": {}}
+
+    @pytest.mark.asyncio
+    async def test_get_set_state(self):
+        storage: DictStorage[Dict[str, str]] = DictStorage()
+
+        key = "L:R"
+        assert await storage.get_state(key=key) is None  # initial state is None
+
+        new_state = "sotm"
+        assert await storage.set_state(key=key, state=new_state) is None
+        assert await storage.get_state(key=key) == new_state
+
+        assert await storage.reset_state(key=key) is None
+        assert await storage.get_state(key=key) is None
+
+    @pytest.mark.asyncio
+    async def test_get_set_update_reset_data(self):
+        storage: DictStorage[Dict[str, str]] = DictStorage()
+
+        key = "L:R"
+        assert await storage.get_data(key=key) == {}  # initial data is empty dict
+
+        new_data = {"sotm": "sotm"}
+        assert await storage.set_data(key=key, data=new_data) is None
+        assert await storage.get_data(key=key) == new_data
+
+        updated_data = {"mpa": "mpa"}
+        assert await storage.update_data(key=key, data=updated_data) is None
+        assert await storage.get_data(key=key) == {**new_data, **updated_data}
+
+        assert await storage.reset_data(key=key) is None
+        assert await storage.get_data(key=key) == {}  # reset_data makes data empty dict
+
+    @pytest.mark.asyncio
+    async def test_finish(self):
+        # finish turns data into initial one
+        storage: DictStorage[Dict[str, str]] = DictStorage()
+
+        key = "L:R"
+        await storage.set_data(key=key, data={"mpa": "mpa"})
+        await storage.set_state(key=key, state="mpa::mpa::mpa::mpa")
+        assert await storage.get_data(key=key)
+        assert await storage.get_state(key=key)
+
+        assert await storage.finish(key=key) is None
+        assert await storage.get_data(key=key) == {}
+        assert await storage.get_state(key=key) is None
+
+    @pytest.mark.asyncio
+    async def test_close_wait_closed(self):
+        storage: DictStorage[Dict[str, str]] = DictStorage()
+
+        storage._data = {"corrupt": "True"}
+        assert await storage.close() is None
+        assert storage._data == {}
+        assert await storage.wait_closed() is None  # noop