Without this check we could end up creating a Track for a .ini file or
some other non-audio file.
Signed-off-by: Anna Schumaker <Anna@OcarinaProject.net>
I move all of the core tests into the core/ directory to keep them
together. Gui unit tests will be put in new directories.
Signed-off-by: Anna Schumaker <Anna@OcarinaProject.net>