StylesXmlAccessor is an abstract class designed to be subclassed for a specific stylesheet. Here, so far, we just want to test one method of the base class, so we make a trivial subclass which trivially implements (by throwing) abstract methods not needed by the one we want to test. The FindOrCreateStyle method is normally called (indirectly) by CreateStyles(), which initializes m_databaseStyles to contain all the pre-existing styles. For this test we just do this in the constructor of our private subclass.
