Add a test for multiple join nodes.
Add a test for multiple join nodes.

dgellis90/nipype,glatard/nipype,carlohamalainen/nipype,fprados/nipype,rameshvs/nipype,mick-d/nipype,rameshvs/nipype,pearsonlab/nipype,arokem/nipype,mick-d/nipype_source,JohnGriffiths/nipype,arokem/nipype,FCP-INDI/nipype,carolFrohlich/nipype,pearsonlab/nipype,carolFrohlich/nipype,FCP-INDI/nipype,grlee77/nipype,blakedewey/nipype,carlohamalainen/nipype,gerddie/nipype,glatard/nipype,FCP-INDI/nipype,rameshvs/nipype,mick-d/nipype_source,carolFrohlich/nipype,blakedewey/nipype,FCP-INDI/nipype,arokem/nipype,JohnGriffiths/nipype,grlee77/nipype,Leoniela/nipype,JohnGriffiths/nipype,iglpdc/nipype,mick-d/nipype,grlee77/nipype,sgiavasis/nipype,dmordom/nipype,grlee77/nipype,fprados/nipype,JohnGriffiths/nipype,carlohamalainen/nipype,Leoniela/nipype,rameshvs/nipype,mick-d/nipype,dgellis90/nipype,sgiavasis/nipype,glatard/nipype,mick-d/nipype,wanderine/nipype,wanderine/nipype,blakedewey/nipype,Leoniela/nipype,gerddie/nipype,carolFrohlich/nipype,iglpdc/nipype,pearsonlab/nipype,gerddie/nipype,sgiavasis/nipype,wanderine/nipype,iglpdc/nipype,wanderine/nipype,dmordom/nipype,iglpdc/nipype,glatard/nipype,arokem/nipype,pearsonlab/nipype,dgellis90/nipype,mick-d/nipype_source,blakedewey/nipype,gerddie/nipype,dmordom/nipype,fprados/nipype,sgiavasis/nipype,dgellis90/nipype