[Test Cases] Missing Test Cases for Patient Command Class

[NCF3535]

Add missing test cases for the PatientCommand class to ensure complete coverage of patient-related functionality. These tests should cover the following scenarios:

1. Add Patient Command:

   • Verify successful addition of a new patient.
   • Confirm that adding a duplicate patient returns the appropriate error message.

2. List Patient Command:

   • Validate correct display of the patient list when it contains patients.
   • Confirm that an empty patient list displays the correct empty message.

3. Delete Patient Command:

   • Test successful deletion of an existing patient.
   • Ensure that attempting to delete a non-existent patient returns an error message.

These tests will improve reliability and prevent regressions by verifying critical patient-related functionalities.