📝 Update docs for testing, fix examples with relative imports (#5302)

docs/en/docs/advanced/async-tests.md

@@ -26,13 +26,23 @@ The important difference for us is that with HTTPX we are not limited to synchro
 
 ## Example
 
-For a simple example, let's consider the following `main.py` module:
+For a simple example, let's consider a file structure similar to the one described in [Bigger Applications](../tutorial/bigger-applications.md){.internal-link target=_blank} and [Testing](../tutorial/testing.md){.internal-link target=_blank}:
+
+```
+.
+├── app
+│   ├── __init__.py
+│   ├── main.py
+│   └── test_main.py
+```
+
+The file `main.py` would have:
 
 ```Python
 {!../../../docs_src/async_tests/main.py!}
 ```
 
-The `test_main.py` module that contains the tests for `main.py` could look like this now:
+The file `test_main.py` would have the tests for `main.py`, it could look like this now:
 
 ```Python
 {!../../../docs_src/async_tests/test_main.py!}

docs/en/docs/tutorial/testing.md

@@ -50,26 +50,58 @@ And your **FastAPI** application might also be composed of several files/modules
 
 ### **FastAPI** app file
 
-Let's say you have a file `main.py` with your **FastAPI** app:
+Let's say you have a file structure as described in [Bigger Applications](./bigger-applications.md){.internal-link target=_blank}:
+
+```
+.
+├── app
+│   ├── __init__.py
+│   └── main.py
+```
+
+In the file `main.py` you have your **FastAPI** app:
+
 
 ```Python
 {!../../../docs_src/app_testing/main.py!}
 ```
 
 ### Testing file
 
-Then you could have a file `test_main.py` with your tests, and import your `app` from the `main` module (`main.py`):
+Then you could have a file `test_main.py` with your tests. It could live on the same Python package (the same directory with a `__init__.py` file):
 
-```Python
+``` hl_lines="5"
+.
+├── app
+│   ├── __init__.py
+│   ├── main.py
+│   └── test_main.py
+```
+
+Because this file is in the same package, you can use relative imports to import the object `app` from the `main` module (`main.py`):
+
+```Python hl_lines="3"
 {!../../../docs_src/app_testing/test_main.py!}
 ```
 
+...and have the code for the tests just like before.
+
 ## Testing: extended example
 
 Now let's extend this example and add more details to see how to test different parts.
 
 ### Extended **FastAPI** app file
 
+Let's continue with the same file structure as before:
+
+```
+.
+├── app
+│   ├── __init__.py
+│   ├── main.py
+│   └── test_main.py
+```
+
 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.