qa: Add guides to test u-boot

Testing u-boot is crucial as it cannot be done in LAVA unless the lab is
updated. In this context, add a guide with useful pointers.

Signed-off-by: Walter Lozano <walter.lozano@collabora.com>

content/qa/testing-guides.md

 +++
 date = "2024-08-30"
 weight = 100
+toc = true
 
 title = "Manual testing guides"
 
@@ -90,4 +91,31 @@ In a similar way, it is possible to set the HDMI as default sink:
 
 ```
 $ pactl set-default-sink alsa_output.platform-120000.hdmi.stereo-fallback
-```
+```
\ No newline at end of file
+
+## U-boot
+
+One tricky component to test is u-boot, as it cannot be easily tested in LAVA,
+as it is tight to the LAVA lab setup. For this reason, when upgrading u-boot
+a strict manual test is required to ensure the the functionality it provides
+works as expected.
+
+U-boot is responsible for the early boot process and preparing the environment
+to load Linux kernel. Also in the OSTree context, it is responsible of checking
+the bootcount and provide the rollback functionality if the bootcount is exceeded.
+
+To properly test u-boot the following steps should be covered:
+- Test APT image on all reference boards to ensure Linux can be booted
+- Test OSTree image on all reference boards, to ensure Linux can be booted
+- Test OSTree image rollback on all reference boards, to ensure Linux can be rolled back
+
+The basic test on both APT and OStree image is to make sure that the system boots
+without issues by following the steps in [Sanity Test](https://qa.apertis.org/testcases/v2024/sanity-check-manual.html).
+
+Testing the OSTree rollback mechanism is a bit more complex. It requires to test two aspects:
+- Bootcount increment
+- Rollback on bootcount limit exceeded
+
+The easiest way to test this is to use the testcase
+[AUM Rollback Bootcount](https://qa.apertis.org/testcases/v2024/aum-rollback-bootcount.html)
+which covers a rollback scenario.