Add test for $Artist format string.
Trivial implementation of $Artist.
Add test for $Title.
Trivial implementation for $Title.
Extract constants in TrackTests.
Add test for $AlbumTitle.
Trivial implementation for $AlbumTitle.
Add test for $AlbumArtist.
Trivial implementation for $AlbumArtist.
Test for combination of specifiers.
Implement proper processing of format string.
Add (passing) test for more complex format strings.
Use ToFormattedString instead of ToString.