Fix `test_tracy.py`'s and `test_search.py` tests from being brittle.

### Description
The current implementation of the `test_getSupervisors` function, in `test_tracy.py`, checks if the people in the demo data are in a predetermined list.
This means that adding any new supervisor to the demo data breaks this test until it is set again. Create an implementation of this that does not require it to assert a predetermined list of supervisors.

`test_getSupervisorsForDepartment`, in `test_search.py`, is also a brittle function in this file. It checks the length of the list of supervisors compared to an expected outcome. This breaks whenever a new supervisor is added to the Computer Science (Department 1) department.

### Notes:
The `test_getSupervisors` looks something like this: `assert s.FIRST_NAME in ['Alex', 'Brian', ...]` and `assert s.CPO in ['222', '888', '6301', ...]`.
This doesn't test whether the function is grabbing new supervisors; it just checks whether the ones in the database are ALL grabbed when the query runs, which is why it crashes when a new supervisor is added.

The `test_getSupervisorsForDepartment` looks like this: `assert len(supervisors) == 12`

Inizia con test_tracy.py's test_getSupervisors e test_search.py's test_getSupervisorsForDepartment, quindi esegui questi test per osservare le assunzioni su nomi fissi e conteggi fissi. Sostituisci queste aspettative fragili con assertions che rimangano valide quando vengono aggiunti Supervisors e conferma che entrambi i test passino con i dati demo attuali.

Scritto dal modello di indicizzazione a partire dal testo della issue.