Write a first Test case for Timer and create a manual for HW tests

[VojtechBartoska]

This issue tracks writing and setting first real test on HW testing framework.

Checklist:

• write an internal Documentation about Test writing
• collect feedback about framework
• propose improvements to HW testing framework if applicable

[VojtechBartoska]

cc @Ouss4 You are already in touch with @P-R-O-C-H-Y, but I just want to sync about Documentation which will be done by Arduino team.

[VojtechBartoska]

All subtasks are done.