Identify the classes and associations in the following narrative, and draw a class diagram with multiplicities:

DR. Franklin runs a small medical clinic specializing in family practice. She has many patients. When the patients visit the clinic, she may perform several tests to diagnose their conditions. She bills the patient one amount for the visit plus additional amounts for each test.

I looked at the textbook solution and saw that the multiplicities on VISIT from the VISIT to TEST relationship to be (0..*). Why is that? For every test there can be no visit? Shouldn't there be at least a visit in order to run tests? I also need the diagram drawn with VISIT, TEST, PATIENT and BILLING.