Add prototype for utils functions

[Joao-Dionisio]

When creating tests it can be annoying having to create the same models over and over again. In this utils.py file, we aggregate some models that might show up more than once.

Note: There is already an util.py file in the tests folder, might want to rename it.

[Opt-Mucca]

I will merge this. The models look good.
Things still to do in some other MR:

• Call them in the actual tests to remove duplicate code
• Merge util.py into utils.py