[yt:backend] add tests for lib

[ascariandrea]

At the moment the coverage for platforms/yttrex/backend/lib is the lowest in the all monorepo.

All files platforms/yttrex/backend/lib

35.54% Statements 305/858
17.87% Branches 42/235
36% Functions 45/125
36.05% Lines 300/832

Tests need to be written in order to reach a reasonable coverage (60%) and then make the ts refactor easier and more secure.