Unit test to check if metrics endpoint is scraping metrics

[vicentefb]

Is your feature request related to a problem? Please describe.
A /metrics endpoint issue was introduced #3920 and there were no unit tests to validate that the endpoint was working and scraping.

Describe the solution you'd like
Testing of the /metrics endpoint and verify all metrics are working and producing results. List of metrics

[github-actions]

'This issue is marked as Stale due to inactivity for more than 30 days. To avoid being marked as 'stale' please add 'awaiting-maintainer' label or add a comment. Thank you for your contributions '