[Testing] [Panther] Add component documentation

.doctor-rst.yaml

@@ -111,4 +111,4 @@ whitelist:
  - '.. versionadded:: 3.6' # MonologBundle
  - '.. versionadded:: 3.8' # MonologBundle
  - '.. _`a feature to test applications using Mercure`: https://github.com/symfony/panther#creating-isolated-browsers-to-test-apps-using-mercure-or-websocket'
- - '.. End to End Tests (E2E)'
+ - 'End to End Tests (E2E)'

testing.rst

@@ -1166,12 +1166,15 @@ HttpClient Assertions
 
  The HttpClient assertions were introduced in Symfony 6.4.
 
-.. TODO
-.. End to End Tests (E2E)
-.. ----------------------
-.. * panther
-.. * testing javascript
-.. * UX or form collections as example?
+End to End Tests (E2E)
+~~~~~~~~~~~~~~~~~~~~~~
+
+If you need to test the application as a whole, including the JavaScript
+code, you can use a real browser instead of the test client. This is
+called an end-to-end test and it's a great way to test the application.
+
+This can be achieved thanks to the Panther component. You can learn more
+about it in :doc:`the dedicated page </testing/end_to_end>`.
 
 Learn more
 ----------