✨ Add docs and tests for Python 3.9 and Python 3.10 (#3712)

Co-authored-by: Thomas Grainger <tagrain@gmail.com>

docs/en/docs/tutorial/testing.md

@@ -65,7 +65,7 @@ Now let's extend this example and add more details to see how to test different
 
 ### Extended **FastAPI** app file
 
-Let's say you have a file `main_b.py` with your **FastAPI** app.
+Let's say that now the file `main.py` with your **FastAPI** app has some other **path operations**.
 
 It has a `GET` operation that could return an error.
 
@@ -73,16 +73,24 @@ It has a `POST` operation that could return several errors.
 
 Both *path operations* require an `X-Token` header.
 
-```Python
-{!../../../docs_src/app_testing/main_b.py!}
-```
+=== "Python 3.6 and above"
+
+    ```Python
+    {!> ../../../docs_src/app_testing/app_b/main.py!}
+    ```
+
+=== "Python 3.10 and above"
+
+    ```Python
+    {!> ../../../docs_src/app_testing/app_b_py310/main.py!}
+    ```
 
 ### Extended testing file
 
-You could then have a `test_main_b.py`, the same as before, with the extended tests:
+You could then update `test_main.py` with the extended tests:
 
 ```Python
-{!../../../docs_src/app_testing/test_main_b.py!}
+{!> ../../../docs_src/app_testing/app_b/test_main.py!}
 ```
 
 Whenever you need the client to pass information in the request and you don't know how to, you can search (Google) how to do it in `requests`.