Add additional test for join attrs.
Add additional test for join attrs.

Dipsomaniac/peewee,Sunzhifeng/peewee,softside/peewee,new-xiaji/peewee,d1hotpep/peewee,ronyb29/peewee,Sunzhifeng/peewee,ghukill/peewee,wenxer/peewee,Dipsomaniac/peewee,Sunzhifeng/peewee,coleifer/peewee,zhang625272514/peewee,coreos/peewee,new-xiaji/peewee,py4a/peewee,wenxer/peewee,jarrahwu/peewee,jnovinger/peewee,jnovinger/peewee,bopo/peewee,teserak/peewee,coreos/peewee,Dipsomaniac/peewee,d1hotpep/peewee,new-xiaji/peewee,coleifer/peewee,mackjoner/peewee,fuzeman/peewee,jarrahwu/peewee,stas/peewee,bopo/peewee,jarrahwu/peewee,coleifer/peewee,zhang625272514/peewee,bopo/peewee,zhang625272514/peewee,lez/peewee,fuzeman/peewee,coreos/peewee