add metadata test
add metadata test

TheOpenDevProject/gmusicapi,nvbn/Unofficial-Google-Music-API,tanhaiwang/gmusicapi,dvirtz/gmusicapi,jimyx17/gmusic,simon-weber/Unofficial-Google-Music-API,thebigmunch/gmusicapi,simon-weber/gmusicapi,peetahzee/Unofficial-Google-Music-API,dvirtz/gmusicapi