Improve test coverage

[alejgh]

We have pretty low test coverage. You can check our codecov review to see the areas where we could make some improvements.

[alejgh]

We can divide the work as follows:

• Carmen: Implement / Improve entities tests.
• Eduardo: Implement / Improve services tests.
• Teji: Implement / Improve util tests.
• Alejandro: Implement / Improve repository tests.

We can change the assignments if you want, just post it here and talk it with the other person you want to make the change with.

[ulitol97]

I'm fine with my assignment. I'll soon work on it (just saying, in case anyone wants to swap assignments).