Introduce the "Debugging a test case" section, in preparation
to the additional flags that will be added in the next patches.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 docs/devel/testing.rst | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/docs/devel/testing.rst b/docs/devel/testing.rst
index 4e42392810..9d6a8f8636 100644
--- a/docs/devel/testing.rst
+++ b/docs/devel/testing.rst
@@ -224,6 +224,14 @@ another application on the host may have locked the file, possibly leading to a
 test failure.  If using such devices are explicitly desired, consider adding
 ``locking=off`` option to disable image locking.
 
+Debugging a test case
+-----------------------
+The following options to the ``check`` script can be useful when debugging
+a failing test:
+
+* ``-d`` (debug) just increases the logging verbosity, showing
+  for example the QMP commands and answers.
+
 Test case groups
 ----------------
 
-- 
2.31.1