Add unit tests to backend

[lealceldeiro]

Is your feature request related to a problem? Please describe.
Not a problem, but right now most of the test are e2e. It is necessary to write unit test for classes that require it.

Describe the solution you'd like
Implement unit test for backend classes using Mockito (maybe consider PowerMockito) for static methods.

Describe alternatives you've considered
https://site.mockito.org/
https://github.com/powermock/powermock/wiki/mockito