Document the asyncio debug option

Author: tjkuson

docs/reference/configuration.rst

@@ -14,6 +14,29 @@ asyncio_default_test_loop_scope
 ===============================
 Determines the default event loop scope of asynchronous tests. When this configuration option is unset, it default to function scope. Possible values are: ``function``, ``class``, ``module``, ``package``, ``session``
 
+.. _configuration/asyncio_debug:
+
+asyncio_debug
+=============
+Enables `asyncio debug mode <https://docs.python.org/3/library/asyncio-dev.html#debug-mode>`_ for the default event loop used by asynchronous tests and fixtures.
+
+The debug mode can be set by the ``asyncio_debug`` configuration option in the `configuration file
+<https://docs.pytest.org/en/latest/reference/customize.html>`_:
+
+.. code-block:: ini
+
+   # pytest.ini
+   [pytest]
+   asyncio_debug = true
+
+The value can also be set via the ``--asyncio-debug`` command-line option:
+
+.. code-block:: bash
+
+   $ pytest tests --asyncio-debug
+
+Debug mode is disabled by default.
+
 asyncio_mode
 ============
 The pytest-asyncio mode can be set by the ``asyncio_mode`` configuration option in the `configuration file