drm/todo: Add entry for using kunit in the subsystem

The Kernel Unit Testing (KUnit) framework provides a common framework for
unit tests within the Linux kernel. Having a test suite would allow to
identify regressions earlier.

Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Maxime Ripard <maxime@cerno.tech>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20220504080212.713275-1-javierm@redhat.com

Documentation/gpu/todo.rst

@@ -603,6 +603,20 @@ Level: Advanced
 Better Testing
 ==============
 
+Add unit tests using the Kernel Unit Testing (KUnit) framework
+--------------------------------------------------------------
+
+The `KUnit <https://www.kernel.org/doc/html/latest/dev-tools/kunit/index.html>`_
+provides a common framework for unit tests within the Linux kernel. Having a
+test suite would allow to identify regressions earlier.
+
+A good candidate for the first unit tests are the format-conversion helpers in
+``drm_format_helper.c``.
+
+Contact: Javier Martinez Canillas <javierm@redhat.com>
+
+Level: Intermediate
+
 Enable trinity for DRM
 ----------------------