Add section about special tags to the unit testing guide

contributing/development/core_and_modules/unit_testing.rst

@@ -240,6 +240,25 @@ the engine, for instance:
             "Invalid HTML notation should result in a Color with the default values.");
     }
 
+Special tags in test case names
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These tags can be added to the test case name to modify or extend the test environment:
+
++-------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------+
+| **Tag**           | **Description**                                                                                                                                                      |
++-------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------+
+| ``[SceneTree]``   | Required for test cases that rely on a scene tree with MessageQueue to be available. It also enables a mock rendering server and :ref:`ThemeDB<class_ThemeDB>`.      |
++-------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------+
+| ``[Editor]``      | Like ``[SceneTree]``, but with additional editor-related infrastructure available, such as :ref:`EditorSettings<class_EditorSettings>`.                              |
++-------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------+
+| ``[Audio]``       | Initializes the :ref:`AudioServer<class_AudioServer>` using a mock audio driver.                                                                                     |
++-------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------+
+| ``[Navigation]``  | Creates the default 2D/3D navigation servers and makes them available for testing.                                                                                   |
++-------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------+
+
+You can use them together to combine multiple test environment extensions.
+
 Test tools
 ----------