Add PersonCardTest
Add PersonCardTest

The GUI tests are system tests.

The individual GUIs do not have unit tests.

Let's add a PersonCardTest to unit test the PersonCard GUI component.

An alternative method of checking the labels would be to use
reflections. However, reflections are not suitable for level 4
learning objectives.

damithc/addressbook-level4,CS2103R-Eugene-Peh/addressbook-level4,damithc/addressbook-level4,CS2103R-Eugene-Peh/addressbook-level4,damithc/addressbook-level4,CS2103R-Eugene-Peh/addressbook-level4,se-edu/addressbook-level3