test(expand): add test against breaking unsubscription chain
test(expand): add test against breaking unsubscription chain

For issue #875.

jadbox/RxJS,kwonoj/RxJS,jayphelps/rxjs,jayphelps/rxjs,kwonoj/RxJS,jayphelps/rxjs,martinsik/rxjs,kwonoj/RxJS,SangKa/RxJS-Docs-CN,justinwoo/RxJS,IgorMinar/RxJS,ReactiveX/rxjs,martinsik/rxjs,gluck/RxJS,Igorbek/rxjs5,jayphelps/rxjs,SangKa/RxJS-Docs-CN,benlesh/RxJS,SangKa/RxJS-Docs-CN,gluck/RxJS,benlesh/RxJS,ReactiveX/RxJS,figueredo/RxJS,adrianomelo/RxJS-1,jadbox/RxJS,RxJS-CN/RxJS-Docs-CN,ReactiveX/RxJS,Brocco/RxJS,Igorbek/rxjs5,Brocco/RxJS,martinsik/rxjs,RxJS-CN/RxJS-Docs-CN,elliotschi/rxjs,saneyuki/RxJS,jinroh/RxJS,robwormald/RxJS,jadbox/RxJS,jadbox/RxJS,staltz/RxJSNext,ReactiveX/RxJS,robwormald/RxJS,ReactiveX/RxJS,gluck/RxJS,elliotschi/rxjs,staltz/RxJSNext,trxcllnt/RxJS,jinroh/RxJS,robwormald/RxJS,jinroh/RxJS,ReactiveX/rxjs,figueredo/RxJS,elliotschi/rxjs,adrianomelo/RxJSNext,jinroh/RxJS,saneyuki/RxJS,justinwoo/RxJS,gluck/RxJS,adrianomelo/RxJS-1,ReactiveX/rxjs,jayphelps/rxjs,adrianomelo/RxJSNext,SangKa/RxJS-Docs-CN,martinsik/rxjs,justinwoo/RxJS,RxJS-CN/RxJS-Docs-CN,trxcllnt/RxJS,adrianomelo/RxJS-1,staltz/RxJSNext,figueredo/RxJS,ReactiveX/rxjs,IgorMinar/RxJS,elliotschi/rxjs,Brocco/RxJS,Igorbek/rxjs5,kwonoj/RxJS,benlesh/RxJS,Igorbek/rxjs5,robwormald/RxJS,benlesh/RxJS,Brocco/RxJS,staltz/RxJSNext,adrianomelo/RxJSNext,adrianomelo/RxJS-1,RxJS-CN/RxJS-Docs-CN,trxcllnt/RxJS,figueredo/RxJS,adrianomelo/RxJSNext,justinwoo/RxJS,trxcllnt/RxJS