[FEAT] - Make units tests on project

[Luckx98]

Frontend acceptance criteria

• [x] Unit tests to subject's, domain, data, infra and bloc.
• [x] Unit tests to review's, domain, data, infra and bloc.
• [x] Integration tests if possible

Backend acceptance criteria

• [x] Unit tests to get all subjects.
• [x] Unit tests to get a specific subject.
• [x] Unit tests to post a review for a subject.

[MauricioMachadoFF]

@LucasSpinosa wdyt is the acceptance criteria for the backend? Please insert here