docs: explain DI container teardown in pytest fixtures

docs/introduction/application-settings.md

@@ -18,8 +18,7 @@ from that_depends import BaseContainer, providers
 
 class DIContainer(BaseContainer):
     settings = providers.Singleton(Settings)
-    settings_casted: Settings = settings.cast
-    some_factory = providers.Factory(SomeFactory, service_name=settings_casted.service_name)
+    some_factory = providers.Factory(SomeFactory, service_name=settings.cast.service_name)
 ```
 
 And when `some_factory` is resolved it will receive `service_name` attribute from `Settings`

docs/providers/resources.md

@@ -4,7 +4,7 @@
 - generator or async generator can be used;
 - context manager derived from `typing.ContextManager` or `typing.AsyncContextManager` can be used;
 
-# How it works
+## How it works
 ```python
 import typing
 

docs/testing/fixture.md

@@ -0,0 +1,21 @@
+# Fixture
+## Dependencies teardown
+When using dependency injection in tests, it's important to properly tear down resources after tests complete.
+
+Without proper teardown, the Python event loop might close before resources have a chance to shut down properly, leading to errors like `RuntimeError: Event loop is closed`.
+
+You can set up automatic teardown using a pytest fixture:
+
+```python
+import pytest_asyncio
+from typing import AsyncGenerator
+
+from my_project import DIContainer
+
+@pytest_asyncio.fixture(autouse=True)
+async def di_container_teardown() -> AsyncGenerator[None]:
+    try:
+        yield
+    finally:
+        await DIContainer.tear_down()
+```